Shattered retreat is good, I will be leaving that on (I hated that wars used to be decided in one battle). Defensive pacts as they are I will switch off, they don't really achieve their goal as designed. I would change them so that same religion will not co-operate with other religions against their own, ever. However, at a high threshold they will work together against a third party. I would also make them offensive at a certain threshold. So we get something like this:
0-25% threat - no pacts
25-50% threat - defensive vs offending religion
50-75% threat - offensive vs offending religion, would be granted a liberation CB against the target that would restore the strongest claimant to each title liberated
75-100% threat - defensive across religions