Well, Thrawns Revenge supports a Rebellion/New Republic side as well, with just as many, if not more ships than the Empire. And yeah, the 'New Republic' does get Y and B Wings, although, later in the game they're replaced by the K-Wing.
Personally, I, being an Empire man, put my faith in TIE Defenders. They can tear apart pretty much any squadron fielded against them, and can hold their own against E-Wings, the best of the Rebel ships. Plus they're Fighter-Bombers. Ion cannons, lasers, and torpedoes.
Rebels best bet is anything with Corellian- in front of it. Their corvettes and gunships are made to shred fighters. But yeah, compared to the vanilla game, the Rebels get tons of new ships. Some of them are even able to go up againt a star destroyer...blech.