I've actually thought more than a few times that the AI is way too eager to join religious leagues.
Half of the European Powers actually stayed out of the 30 years war completely or at least had very minor participation (Ottomans and PLC did little outside the 1 year Polish-Ottoman war, Muscovy stayed out completely IIRC, Portugal was busy as Spain's lapdog in the 80 years war). And then again half of the nations which did get involved directly never committed nearly as much resources as every league war in game represents (France joined the war rather late, England gave mainly economic support).
But in every single game ALL of the European powers join one of the sides, then beat eachother silly during an all out war that rarely lasts more than 10 years...
Wouldn't it be nice to have a lower intensity war going on for longer, with nations joining in and dropping out, and even switching sides?