Biggs really is just fine. He has been in the game since Wave 1 and he wasn't a super big (haha) then. He was around certainly but he wasn't the only option. Of the three Paul Heaver World's winning Rebel lists, Biggs was only in one. And I don't think anyone would say, even back then, that Biggs walks the Dags was an overpowered list. Biggs only became almost mandatory in Rebel lists when the game's alpha strikes flew through the roof.
Likewise, Biggs doesn't need to be nerfed in order to buff the T-65. It was already pointed out that a maneuverability buff would not help Biggs at all. Likewise, anything that requires you to put a lot of points into a ship wouldn't help Biggs as part of the reason he is so good is his 26-27 price point. Spending 35 points on Biggs isn't something that is likely to be done (or if it is, you will be getting what you pay for but be much more limited in the rest of your list).
Miranda or Sabine would be better places to look into for a Rebel nerf. Or TLT. Most certainly TLT.