Skiprays' jamming ability is pretty useful against them, too. So is the Crusader's point defense. The Zann Consortium can stand up to MC-30s pretty well.
I imagine that VSDs could make a pretty big dent in an MC-30 fleet. As for the ISD being weak against TIE bombers, that's just an encyclopedia suggestion. Other ships could be effective against the ISD as well. I like the idea of the Rebels having a small capital-ship-killer in their arsenal.