you are continually making the assumption that arbitrarily adding points is somehow accurately representing what you as an individual player accomplished in a game. this is not true and i'm not sure under what basis you're concluding that it is
there is no accurate way to determine what a player's performance actually contributed to in a game, which is why judging purely based on whether your team won or lost is the only thing you can do to measure skill. adjusting this value just to guarantee points are gained even when unnecessary does not measure anything at all; you could have contributed nearly nothing to a game and won it due to it being a game you were expected to win anyway, and with the new system, you still gain points for that, when the older system would more accurately determine that your rank should not be affected much by that game since you were already predicted to win it
essentially, the crux of your argument is that s3's system accounts for in-game factors that s2 doesn't, when it is clearly the case that a flat addition of points regardless of the difficulty of the game is not actually accounting for those factors at all
it's pretty easy to determine that splatoon 3's system was changed to make x-rank feel more fun to climb. because that's what it accomplishes, and that's what nintendo benefits most from: it encourages people to play the game more. it would be perfectly reasonable (and, in my opinion, more interesting) to debate whether or not that approach is better than an approach that favors accuracy over emotions, but you're instead arguing that s3's system is somehow more accurate to player skill than it was before, when it's fairly trivial to conclude otherwise
worth responding to this too: at least for me i can say i am not nostalgic for s2 at all, because i never played that game. splatoon 3 is the first splatoon game i've played, but i can critically analyze the difference between the two formulas and pretty confidently conclude that s3's is very simply biased towards extremes in a way that s2's wasn't. i'm just debating it because i do feel like there's an objectively true conclusion to be made about this and it's less interesting than the other stuff we could be discussing about it