I think you got it all the wrong way. The best fix might be the one that sounds most complicated at first: Fixing the targeting algorithm.
If a squad's target is set to anything else than "Large Monster", squads with only 1 single unit in it should be ignored, unless there is no other target at all.
Mages obviously must be handled a bit different. But they already choose their spells dependent on how much damage they do to the target. So it's simply a matter of giving them better chances to actually do some damage at all: Atm, bolt spells are mostly useless against single targets, as they usually hit
the right square only 30% of the time. And then can still fall on an unoccupied slot, or be blocked by a shield. If low-level bolt spells would have
way higher accuracy, the IMHO the mages would use them automatically to fry any decoys in range. And as the spells have low path requirements, fatigue gain would be small.
Btw., IMHO this fix has the biggest chances to get implemented: One of the devs said once it's much more fun to fiddle with the AI than to alter the Ui or code new battle mechanics
