What are you playing and where are you stuck?
Christ, I can't play fighting games for shit.Ohh... Yeah, I have the same issues. I think there's a certain rhythm to them where the next button press can't be too soon after the previous. But you also have to be quick because the opponent will do something which stun locks you as a hit animation plays out. So you wind up with a window of a few frames where any input is accepted. I'm terrible at rythm based game mechanics so I never felt like I understood how to play well enough to realize what I was doing wrong.
Yeah, the people that typically play fighting games online typically devote themselves to one fighting game. While some ridiculously amazing fighting game players can play multiple games at a high level it's rare. In the old days before online gaming was a real thing, people would kid themselves at being amazing at say Street Fighter II because they could beat their friends or at their local arcade they were best. Online play makes people realize how much better people can be at games like that.
A great example of this is Starcraft, to be damn good at that game you have to have a high APM even if you know the game in-depth and know build orders and how to manage the units well. Without a high APM you will never be a tournament level Starcraft player.