The only real teams that should require Overprepared are teams that would naturally be prepared in canon, like Rebels (Phoenix) or First Order (they built an entire army in how many years?). There's also teams that need the speed to be viable, like Jawas and Tuskens (it's an ambush but there's nothing really ambush-y about the fight?).
Every other team should have their own unique modifier that challenges the player in its own unique way and encourage team switches and mod challenges; after all, the more you make the player change stuff around, the more energy they'll waste and the more money they'll spend on refreshes. It's just good business, and good game design