Yeah Muslim's are a bit op'd in 1.06 with holy wars. They need to something to balance it out as in having a unified Christian response to Muslim invasions (I mean that was what the Crusades started out as).
My argument is that it is too easy to blob as Christian and Muslim and there needs to be something to balance it out. Either make autonomous vassals more atonomous or give each side a unified response to mulsim/christian holy wars. As many pointed out that Alvorids (sic?) always take souther France in one big gulp without as much as a finger lifted by the rest of Christendom.