So AI ally actually gets to do some wars of its own instead of being player's/another ai's wrecking ball 24/7.
I remember seing in one DD (unless i imagined it

) that you said you would try to make AI smarter to not get used by players to fight player's wars all the time. Plus one for this change.
There should also be some metrics of how much is the player involved in AI wars, ie. if player is just sitting and not helping AI should know, relations should drop and in worst case AI need to break the alliance. Metrics should be something like : number of battles joined from total number of battles, units killed and lost, AI is losing war - should be worse for the relation with a player if not helping, AI winning war should make AI forgiving for players non-involvement, distance - AI should not expect much help in trans-continental wars etc... These all could be built into Trust modifier, but it should be transparent to the player at the end of the war - like saying: "You gained/lost X trust towards AI due to: responding to call, joined battles, occupations, giving territory etc..".