How far do you want to take this? There are people who are unable to progress beyond a single screen of every game that has ever been made. That is not proper argument for the design space of a given game (or genre).
Think of it like a linear graph plotted by every possible input combination and a successful output coming out the end. On the far left side, there is a game where you press any input and you achieve a success state. On the right side, something so complex, no human mind could comprehend. Brawlers, exist much further on the left side than fighting games. Many genres exist further to the right of brawlers, RTS games, 4x games, some strategy and RPG games, competitive FPSs, among many others. Saying someone can see the merits of design depth/complexity of fighting games as compared to RTS games makes sense. Saying that they should see it in Brawlers doesn't.
I don't like the input and success state comparison. If you're going to measure depth, you have to measure the difference between the most skilled and least skilled players, even in games that aren't directly competitive. We'd have to establish the best way to measure skill at a belt scroller (it might be for score, it might be by some other player-chosen criteria in the case of throwaway scoring systems, etc). It isn't simply a matter of reaching the end game credit scroll unless that's also how you want to measure fighting games. Of course, we measure the complexity of fighting games by judging human versus human matches. I absolutely assume fighting games have a bigger gap, though I'd put the well-made arcade belt scroll games to the right of, shit, quite a few genres.
Anyway (lol), I never compared them to fighting games. I was solely addressing your doubt that someone could be measurably "good at" a game like Streets of Rage. It's so utterly obvious that they could, even if they are simpler than the spectrum of human fighting game competition.