Enemies with no weaknesses are not cool Larian (except for Madara) ... they are only frustrating.
I am sympathetic to your argument in general, but I found the "Grym, Eternal Protector of the Forge" fight to be enhanced by its complete and utter lack of weaknesses. I don't like how DnD can almost default into a core gameplay loop of just lowering HP with whatever moves you have. Enemies without weaknesses can be fun by forcing you to get creative outside of how you do other fights, as long as they incorporate some other mechanic that gives you a fighting chance.
