i avoid fighting games in general because they're all built upon a terrible system of mechanics called real time combat. so no, i cant really tell the minor tweaks they made between the successive street fighter versions. if they completely overwrote the entire combat system then i guess that's one of the outliers of the edition creep
i have however played the first 3 smash games and the only thing they ever added was new characters and changes to the game's flow. obviously melee is the superior of the 3 so i dont see why anyone would ever purchase brawl or n64 unless they bought it as a kid out of the same blind hype joy that people get for no reason over smash games. even as an 'ok' fighting game melee is still awful to play and suffers from all the same unfixed issues that all other fighting games suffer from, namely a lack of choreographing
I mean it's okay if you don't enjoy the concept of fighting games but I don't understand the difference between "real-time combat" and "choreography" or what those specifically means as it pertains to a fighting game combat system so you'd have to elaborate what an overwritten fighting game would play like.
New characters are usually the main draw for a crossover series and by proxy a fighting game series so I'm not exactly sure how that comes across as an insignificant change. The game's flow is also one of it's most important changed because that's what differentiates fighting games from title to title and series to series.
Also people usually buy new games in a series because they are new and have features unique to the series. It's funny that you mention Fallout and RE building their games ground up when both series have later titles that are just not as good as the others, but still their own unique experiences worth playing. There's nothing hype about buying a new game in a series with installments 4 or 5 years apart except for the time-between aspect.
Again you'd have to actually say what the issues every fighting game has supposedly before any critique of the entire genre makes sense.