"Teganze: life leech now works, removed autospawn, 100% chance to get global monster buff (from 75%). Removed elemental pierce and balanced around 80% res."
Unless it is only a display bug there is no way to increase merc's res cap above 75%, and summons/builds utilizing meatshields suffer from this change. My tankily geared merc went from never dying in Teganze to instantly dying, and my acid fiends die way more frequently drastically slowing my progress.
It might be worth considering giving mercenaries an intrinsic res cap of 85 or 90 and/or adding max res to the summon res mystic orb. Nobody enjoys constant resummoning/rehiring, but I understand there are a lot of balance considerations to be made.