+1 that the idea is very good but the execution is...questionable at best. Weapon abilities should give much-needed flexibility (and weapon identity) to martial characters without being strictly more powerful options or stepping on the toes of other classes' features. The current special attacks satisfy neither of those criteria.
Larian needs to be vary wary about weapon abilities that mess with the action economy (bonus action cost and/or stunning the enemy) and need to include an appropriate drawback for each ability. E.g., doesn't do damage, attack at disadvantage, etc.
Of the moves that are currently present in the game, Brace is probably the best example of how it should be implemented. You sacrifice most of your movement to get advantage on damage rolls, so there is a drawback (your mobility for the turn is heavily limited) coming with a bonus that's considerable enough to compensate. Maces spending a reaction to do some damage even when the attack misses is an interesting concept as well, making them a viable choice for a character that dumped both strength and dexterity.
