+1
I'm in favor of additional abilities that offer positives but that also come with numerical negatives. I like your ideas OP, though they probably would require some fine tuning: e.g., go for the arms shouldn't require you to physically stand on the side of an enemy. That's too finicky and precise.
These abilities could be instead of or in addition to the weapon abilities already in BG3 (you have a bludgeoning-specific action in your list). Weapon ability cooldowns don't really make sense, so making them include penalties to attack or AC or provoke an AoO makes more sense. Aside from the cooldowns and the fact that some weapon abilities in BG3 are much better than others, these are one of Larian's homebrew I like most.
D&D in previous editions had these additional attack options (or at least, Pathfinder has them) and it's a shame that they disappeared in the simplification to 5e.
I feel about the same. I miss the older "Called Shot" system that allowed for special attacks with a penalty.
I'd said elsewhere I'd like to see the weapon specific attacks updated a bit and maybe added to. Some of the ideas may not be 5e, but as far as homebrews go at least these are in line with that older system.
One big special ability I haven't seen yet in BG3 that should be there, especially for martials, is a disarm. That is a 5e thing.
