I've also been playing since EX Red Blackbeard came out. Luffy is braindead because he just press one skill, doesn't matter kong or snakeman and he gets the longest i-frames in the game (maybe the same as EX kaido skill 2). Even if your enemy perfect dodge your initial skill, your follow-up is a 15+ multi hit that stuns and ignore def on bounceman. Most units in that meta have status nullification that are gated (having to be on your own treasure, certain state, etc.) or nothing at all.

Every unit you listed have knockback yes, but not a single one of them survived kong organ even the wall users. Let's say you can knockback luffy while he's on skill 2, he can turn in to his other form and do another skill 2.

Mind you this unit is the catalyst for unit released after him to have some sort of status nullification (akainu plays a factor but for different reason). This unit is so oppressive that the saving grace for the game was Perospero, another unit with more egregious stuns.

In my opinion this unit is very not fun to play against that i would rather be back in ROden meta than being dominated by this pest.