In actuality it being 20% is a net negative and further enforces the notion of rng being the main issue here and not something as simple as a switch in moves or the addition of random coverage. Take for example the fact that 80 percent of the time tusk ko's ursa but there is a chance this simple dynamic flips on it's head and now the much slower ursaluna ko's it, this is definitely not something competitive and adds nothing of value to the metagame other than making players play a game of 80-20 on top of more rng bs
EDIT: QC has already been banned in other formats of ou like dpp ou
as seen here here is an excerpt from one of the moderates talking about QC's uncompetitive nature
"It is uncompetitive because it takes the game out of the better players hand a surprisingly high amount of times. While the chance for an activation is "only" 20% over a single turn, usually you have it on mons that have the bulk to be around for more turns and get the activation. You would usually put it on mons like Metagross, Machamp, Tyranitar etc who have high dmg output and OHKO potential while having the bulk to be around for a few hits. Especially in the case of Quick Claw on Machamp with Dynamic Punch activating that can just be detrimental to any sort of game plan one can make. There is no counterplay to it other than pray. add to that the fact that even if there was counterplay you cannot assume that quick claw is coming your way, since you would expect people to use more reliable items. I have a few replays from both myself and others to showcase games where the better player lost because of quick claw. "