Before I go into actual comparisons, just look at what the transfer did. Same Spd base as Haar but 15% higher growth, and only one below Oscar himself. 50 HP base (3 from capping) and 24 Str base allows him to 2HKO Warriors in 3-P with a Steel Axe and Halberdiers with the Short Axe, as well as being in 4HKO range on Generals with the Killer Axe (So a crit + hit kills). Oscar always has lower Str and always uses weaker weapons.
But the Spd saves Oscar, right? Well, not entirely. 21 Spd doesn't double much in 3-P and 3-1 that 20 Spd doesn't (A few Sages and Generals [lol at Oscar attacking them], and then some with 16 AS also). The following is going to be a bit of a longshot, but I'm trying it anyway. Speedwing on Boyd at 3-2. Assuming he did not gain a Spd level yet, this allows him to double a whopping 39 enemies he couldn't before. Assuming he did get Spd, he can now double 23 more enemies (Same guys + a Halberdier). It isn't as epic as that in the next few maps, but it pretty much allows him to double Generals and Sages forever where he would've been very borderline or outright not doubling before, and doubling Generals with his naturally massive Str, Fire affinity, and Axes I'd say is a good thing since a lot of units have trouble dealing significant damage to them.
Here's the controversial issue: What about the competition for a Speedwing? Well, it was previously decided that Titania and Haar (w/Crown) are the Wing candidates, and only two Wings are available. However, this is Boyd (T) we're discussing, so his team will have other transfer units. Is it fair to assume his team will have Titania (T) as well, and therefore she won't need a Wing? I'd say it's reasonable to assume so given how well the combination would work out in the end. Either that or perhaps Boyd (T) taking a Wing to double is more efficient than Haar taking a Wing and Crown to double.
But what about Oscar? Well, I think it's pretty obvious that as long as both or neither double (and since the Wing ties their Spd or pulls Boyd ahead and Oscar caps it fast while Boyd goes higher, this will only tip in Boyd's favor) Boyd will be doing more damage. Durably, Boyd has 12 base HP while Oscar has 2 Def, 5 Res, 7 base avoid, and Earth affinity. Growth wise, Boyd beats Oscar in Def by 20% (Boyd's HP caps in 3 levels, so that's not worth mentioning here), so that gap will close (lv 16 Boyd and 18 Oscar have roughly equal Def, Boyd winning by .2) and the HP gap only gets bigger.
The affinity is a major advantage for Oscar, right? Well, sort of. Funny thing is that their best partners are likely going to be each other. Oscar desperately needs the atk boost and Boyd doesn't need much aside from what his own affinity gives, though the avoid is obviously nice. They also have the brotherly Bond for +10% crit each, which will stack nicely with Killer weapons.
Things go like this for a while. Both mostly double the same stuff until nearing promotion where Boyd wins, then Oscar promotes and might win (still notably less Str even with BEXP help, and Sol sucks), then Boyd promotes and beats him to the ground (BEXP can help him get more Spd) for the rest of the game. 20/1 Oscar will have 26 Spd, it's almost guaranteed and can only go lower anyway. Boyd will have 29. If this happens by 3-E, 29 AS doubles everything except 3 SM's. 26 only misses a few enemies (all SM's and a few others), but Boyd is clearly winning. (btw, level 18-19 Boyd in 3-10 and 3-11 was doubling most everything anyway, so if Oscar won at all before promotion it wasn't by a lot).
EDIT: Actually, I forgot to add the transfer (or the Wing, I guess) when I was looking at some numbers, and level --/17 Boyd already ties 20/1 Oscar in Spd, so promoted Oscar never really has an advantage aside from 13% Sol activation, but level 17 Boyd is already ORKOing everything he doubles in 3-10 and 3-11 (Note that he doubles everything aside from SM's and bosses, even Halbs and Warriors) even without his support bonus sometimes (Even Generals with a Steel forge/Poleax), though he needs the support for them). So unpromoted Boyd is still > promoted Oscar since 100% ORKO (or whatever it is with Boyd's Hit rate) > Oscar's ~24% chance on whatever he doesn't 2HKO while doubling (which Oscar needs crazy high Str, max MT Steel forge and a +atk support to do most of the time [only the Str is questionable, the forge is fine and Boyd provides the support]).
Come the rest of part 4 and Endgame, it's too obvious. Oscar never closes that 3 point promotion Spd gap since he caps too fast and Boyd always does more damage for obvious reasons (more Str, stronger weapons, better mastery activation, and more crit). Boyd can double all Spirits from ~20/11 while Oscar can only double Thunders. Boyd can use Nasir to double Auras (and, IIRC, ORKO some) while Oscar...can't.
Now, I realize I left out +2 move and Canto, but I don't honestly think that's going to let Oscar pull a win since Boyd (T) cleans him statistically for like the entire game as long as he can get a Speedwing. He probably even wins at times without a Wing, who knows? (EDIT: Later in part 3 and part 4 he does) And then Boyd also becomes superior durably if he wasn't already (12 HP is a lot), so it would be safer to send Boyd into enemies rather than Oscar anyway. In fact, if the Wing is acceptable, I could see Boyd (T) going a lot higher, since doubling with his high Str would put him on a similar level to Gatrie with less durability and somewhat less Str but with better mobility.
I'm tired now, so read and discuss. If Boyd (T) > Oscar is accepted, this can be a topic about Boyd (T) to see how much higher he can go.
But the Spd saves Oscar, right? Well, not entirely. 21 Spd doesn't double much in 3-P and 3-1 that 20 Spd doesn't (A few Sages and Generals [lol at Oscar attacking them], and then some with 16 AS also). The following is going to be a bit of a longshot, but I'm trying it anyway. Speedwing on Boyd at 3-2. Assuming he did not gain a Spd level yet, this allows him to double a whopping 39 enemies he couldn't before. Assuming he did get Spd, he can now double 23 more enemies (Same guys + a Halberdier). It isn't as epic as that in the next few maps, but it pretty much allows him to double Generals and Sages forever where he would've been very borderline or outright not doubling before, and doubling Generals with his naturally massive Str, Fire affinity, and Axes I'd say is a good thing since a lot of units have trouble dealing significant damage to them.
Here's the controversial issue: What about the competition for a Speedwing? Well, it was previously decided that Titania and Haar (w/Crown) are the Wing candidates, and only two Wings are available. However, this is Boyd (T) we're discussing, so his team will have other transfer units. Is it fair to assume his team will have Titania (T) as well, and therefore she won't need a Wing? I'd say it's reasonable to assume so given how well the combination would work out in the end. Either that or perhaps Boyd (T) taking a Wing to double is more efficient than Haar taking a Wing and Crown to double.
But what about Oscar? Well, I think it's pretty obvious that as long as both or neither double (and since the Wing ties their Spd or pulls Boyd ahead and Oscar caps it fast while Boyd goes higher, this will only tip in Boyd's favor) Boyd will be doing more damage. Durably, Boyd has 12 base HP while Oscar has 2 Def, 5 Res, 7 base avoid, and Earth affinity. Growth wise, Boyd beats Oscar in Def by 20% (Boyd's HP caps in 3 levels, so that's not worth mentioning here), so that gap will close (lv 16 Boyd and 18 Oscar have roughly equal Def, Boyd winning by .2) and the HP gap only gets bigger.
The affinity is a major advantage for Oscar, right? Well, sort of. Funny thing is that their best partners are likely going to be each other. Oscar desperately needs the atk boost and Boyd doesn't need much aside from what his own affinity gives, though the avoid is obviously nice. They also have the brotherly Bond for +10% crit each, which will stack nicely with Killer weapons.
Things go like this for a while. Both mostly double the same stuff until nearing promotion where Boyd wins, then Oscar promotes and might win (still notably less Str even with BEXP help, and Sol sucks), then Boyd promotes and beats him to the ground (BEXP can help him get more Spd) for the rest of the game. 20/1 Oscar will have 26 Spd, it's almost guaranteed and can only go lower anyway. Boyd will have 29. If this happens by 3-E, 29 AS doubles everything except 3 SM's. 26 only misses a few enemies (all SM's and a few others), but Boyd is clearly winning. (btw, level 18-19 Boyd in 3-10 and 3-11 was doubling most everything anyway, so if Oscar won at all before promotion it wasn't by a lot).
EDIT: Actually, I forgot to add the transfer (or the Wing, I guess) when I was looking at some numbers, and level --/17 Boyd already ties 20/1 Oscar in Spd, so promoted Oscar never really has an advantage aside from 13% Sol activation, but level 17 Boyd is already ORKOing everything he doubles in 3-10 and 3-11 (Note that he doubles everything aside from SM's and bosses, even Halbs and Warriors) even without his support bonus sometimes (Even Generals with a Steel forge/Poleax), though he needs the support for them). So unpromoted Boyd is still > promoted Oscar since 100% ORKO (or whatever it is with Boyd's Hit rate) > Oscar's ~24% chance on whatever he doesn't 2HKO while doubling (which Oscar needs crazy high Str, max MT Steel forge and a +atk support to do most of the time [only the Str is questionable, the forge is fine and Boyd provides the support]).
Come the rest of part 4 and Endgame, it's too obvious. Oscar never closes that 3 point promotion Spd gap since he caps too fast and Boyd always does more damage for obvious reasons (more Str, stronger weapons, better mastery activation, and more crit). Boyd can double all Spirits from ~20/11 while Oscar can only double Thunders. Boyd can use Nasir to double Auras (and, IIRC, ORKO some) while Oscar...can't.
Now, I realize I left out +2 move and Canto, but I don't honestly think that's going to let Oscar pull a win since Boyd (T) cleans him statistically for like the entire game as long as he can get a Speedwing. He probably even wins at times without a Wing, who knows? (EDIT: Later in part 3 and part 4 he does) And then Boyd also becomes superior durably if he wasn't already (12 HP is a lot), so it would be safer to send Boyd into enemies rather than Oscar anyway. In fact, if the Wing is acceptable, I could see Boyd (T) going a lot higher, since doubling with his high Str would put him on a similar level to Gatrie with less durability and somewhat less Str but with better mobility.
I'm tired now, so read and discuss. If Boyd (T) > Oscar is accepted, this can be a topic about Boyd (T) to see how much higher he can go.