Seems its more a problem with modifiers giving armor or heavy armor to enemies, making some builds unviable (like the swarm of vivisectors from techno adept, and eventually any build without armor piercing)
I´ve already run into few missions i just cannot complete in any way because there are unkillable enemies, getting totally zero damage. There should be always at least a minimum amount of damage done to prevent missions of being predestined to fail.
I guess the game wasn´t intended to put a player in a situation like this, and may be a design overlook, not a "feature".
Thanks in advance.