The thing is Spike fixed most of the problems with BT3's roster, accept for some reason they just had to keep Vegeta "Scouter", Majin Vegeta, Ultimate Gohan and Trunks with the sword separate from there main personas. If would make since to keep Vegeta from the saiyan arc separate in BT3 if only because giants were playable and it may've been hard to incorporate his Oozaru form with the others. Since there were no playable giants in Raging Blast they coulee combine ALL of them, he doesn't seriously fight in his base after the Freeza arc any way so his Saiyan/Namek arc move set could've been used for his base form. I believe that the current gen systems are powerful enough to allow Vegeta's Oozaru form to be part of his transformation set it could just be irreversible like his Majin form but now that I think about it Baby could transform to his Oozaru form just fine... DAMN YOU SPIKE!!
As for Trunks he barley use his sword.. he killed Freeza with it, he tried to hit 18 with but to no avail and in the series he hadn't used it since. He used it in movie 7 but only to deal the finishing blow to 14 and have it shatter against transformed 13. While he had the blade he was no Kenshin, hell he was no Yajirobe so I don't know why Spike likes to treat him as such. Have Burning Slash as a customizable finisher with his Super Saiyan form and the sword it self could be used as like a signature move or something.
Ultimate Gohan? Irreversible transformation.. that is all.
Metal Cooler and Freeza? have the item equipped liked the Budokai games or again.. irreversible transformation.
As for GT like some of you already said the main villains, Bebi (Vegeta), Super 17 , 3 star, 4 star and 1 star Dragons. I don't need to play as the sigma force or Rildo, or Ledgic but I guess they are about as import an as the Ginyu force was... then again no the Sigma Force was not as important as the Ginyu Force, Rildo maybe Ledgic is about as import as Dodoria so he up for grabs I guess. To be honest I don't need to play as Kiwi, Saibamen or Cell jrs either.
Dragona Ball? just the Villians are fine imo and Kid Goku of corse, kid Krillin eh maybe he could be his own character because it would be sort of weird to see him do Kienzan as a kid if it was just a costume. But yeah villains, Daimao, Tambourine, Tao and Blue.. and Roshi too I guess.
EDIT : That SD scan is hilarious

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Peace and Power Kevin Samuels