Combine the two ideas. A successful AP victory vote means a crusade; anyone with the AP religion gets vassaled to the winner (a human player loses); anyone who's an AP member chooses to vassalise or not (the AI, based on diplomacy relative to the winner; a human can't because a human can't vassalise). If a civ's an AP-vassal it can't change state religion or switch to FR; the AP vassalisation is broken only if the master forsakes the AP religion, which the AI won't do unless they're losing. Severe diplomatic penalties with the civs that don't end up as AP-vassals. (I have more than a paragraph of this idea, but that's the potted summary).
Now, with one fell stroke, the AP is less annoying, you have bone-fide crusades, and it's certainly not less balanced for the player to exploit. (Now, if you pull off an AP cheese, you win. In my proposal, you got a good shot at a win.)