So if I understand you correctly the problem is that a lot of units in X-Com-Files are set to aggression 2 or higher and this results in a behavior which you consider as too aggressive, when the option to inherit the aggression from the unit is enabled.
Hi, Xilmi!
I think it worth considering to link aggression to the ranks, except cryssalid and zombie behavior, who should be considered as walking weapons. E.g. in the first player's turn AI checks the battlefield ranks and randomizes aggression for each unit, depending which role should they get.
If dog/zombie/cryssalid/degenerate brute - then straight-forward
If it soldier/tank - then some pushing behavior,
If it engineer/medic then some covering behavior,
If it commander, "prefer to keep safe" behavior
If it mind-control unit, then mixed behavior
Nevertheless, it is very intriguing: will you implement at least some frustration between enemy troops given that 70-95% operations are started by X-COM and only 5-30% are started with enemy (the retaliation, terror missions, environmental alerts, gang attacks etc.)
If then modders provide some flags for types of missions, some missions will contain 100% combat-ready enemy AI, and some (that are initiated by X-COM) will contain certain amount of "frustrated/ambushed/wtf is going on' enemies. That will, in it's turn, bring missions closer to real life behavior and somehow get mods possible to play for joy at difficulty level higher than 1.