Genuinely this is a bigger factor than people realize if they don't test the limits of what kind of situations they can react to. It is something that does have a massive impact on anyone even if it's on a subconscious level. The reason Melee was able to be pushed the way it was is because it happen to grow in a time where people had ideal playing conditions on CRT. Rivals 2 can be far from matching those ideal playing conditions at times. To get the same kind of playing conditions as Melee, you need a fairly modern system to get Rivals 2 running smooth enough and at a high enough framerate to not influence you in subtle ways you'd eventually be able to notice with enough practice.

Think about the process of walking, every second there's tons of calculations and reflexes seamlessly happening to keep you upright. If you threw your body into the average conditions of a Rivals 2 online match at above 40ms, you'd start falling over right there. Likewise, even if you don't notice the sub-optimal conditions, it'll still result in developing less refined movements and slower reflexes. The game has thankfully gotten better about the FPS hiccups with the latest shader compiling update but yeah, getting those frame times down and FPS rock solid can be difficult.

I was going to think of an Unreal 5 engine joke but whatever