Someone else should speak to Pokémon, since I've long since stopped playing that and did very little multiplayer even back when I did play it, but you're simply wrong about Smash Brothers. The reason that competitive play in Smash uses only certain elements of the game is in order to make the competition as fair as possible - to remove random elements that can make it no longer a competition of skill between two players, but significantly impacted by mere luck, or elements that can create unpleasant gameplay in a competitive environment*. And the series has always supported that, by allowing items to be toggled on or off, or allowing you to pick which stages you want, even in Smash Ultimate allowing you to turn off stage hazards separately from simply selecting stages that don't have hazards. So to claim it goes against the game's design is just silly. The games are absolutely designed to support that kind of play, and have been since the very beginning.
Basically, Smash Brothers is designed to be played however people would like to play it, with options aplenty. It's absolutely silly to claim there's any one true way to play it, or pooh-pooh other people playing it in a manner you wouldn't choose to play. Play it how you like, and let others do the same.
Also, for the record, a fair amount of people who play Smash competitively do also play other fighting games competitively. For example, one of the best Smash Melee players in the world, who goes by the name Leffen, is also well-known these days as one of the best Guilty Gear Strive players in the world, and I just watched him place 4th in a big tournament for that game this past weekend.
*Stages with walk-off edges, for example, where players could just sit by the edge of the stage, grab the opponent, and throw them off for a quick KO, repeatedly, turning the whole game into a brief flurry of near-instant-deaths. That would be the optimal way to play on those stages if your goal is to win, since it gets you kills the quickest, but nobody truly wants that kind of gameplay experience, so those stages aren't allowed in competitive play.