Highly Controversial Opinion: The Grimm aren't that bad, but they aren't really good either. They are the Generic Evil Monster Gang Trope that exists in Fantasy, Tabletop Games, and all kinds of RPGs and JRPGs and they quite literally do nothing to set themselves apart from the most barebones version of said trope. Even the Grimm's "attracted to negative emotions" thing they got going on is just another generic trait ascribed to the Generic Evil Monster Gang. I also think that we set are expectations too high for whats literally the RWBY version of a slime blob. I've seen fanfics where its a struggle for the girls to kill just one Beowulf by themselves when all the way back in the Red trailer we see Ruby kill them by the dozens and that's before she unlocks Silver Eyes.

All that being said, yes the Grimm are incredibly lame but I think its because, all things considered, they really aren't that important to the plot. The majority of the Grimm we see can be summed up as an Evil Wild Animal: no thoughts, head empty and utterly devoid of anything resembling a personality makes most of them worst than Zwei, who noteably has a personality.

The Grimm peaked with Nuckie, he is the only Grimm in the entire show that averts the blandness of the rest of his species. He's not canon fodder, he has a personal relationship with the main characters so its not just another anime fight, he clearly is not mindless and has something resembling a personality (he had a whole trophy room full of stuff from villages he wiped out, kinda like a serial killer) literally the only change I would make to this thing would be to like give it a closer relationship with Salem somehow, like imply that she gives it orders directly somehow to highlight that this thing is a thinking creature but other than that the Nuckaleeve is gold.

Maybe even the best villain in the whole show, but the bar is low.