The difference is the number of games to build pattern knowledge and what is "lost" during that time, whether this is correspondence or with peers on a physical board.
You could play corr and play eg a lot of slow Berlin games and a lot of slow open Ruy games and a lot of slow Breyer games and a lot of slow Zaitsev games and a lot of slow Chingorin games, a lot of slow Marshall games plus a few for the sidelines.
The alternative is to spend that time in technical endgames, visualisation and calculation, tactics, high quality training material eg Dvoretsky. Playing a d3 Ruy or an Italian frees up this time.
The later being the more likely to improve your game than spending this time on the Ruy.
A coach I know personally, himself a well regarded author of a couple of opening monographs ( targeting 2200+ audience) had told me that two of his students broke 2000 ( fide, not chess.com ) with zero opening knowledge, they were playing really just developing moves.
Most of his students, esp those above 2000 typically do have a defined repertoire but it's one that allows them to focus on the important part of the game and not on repertoire maintenance nor theoretical lines.
None of them play the Ruy actually, some are FMs, there are a couple of IMs there too, so this time is probably better invested on the Dvoretskys, and well annotated games instead of going after theoretical openings.
You say that I'm promoting my favourite openings. That's true but they are not just my favourite openings. They are also the chosen weapons of many of the strongest GMs throughout history. These are top quality openings and also very enjoyable.
You just want everyone to play openings like Exchange Ruy Lopez and Exchange French. You promote playing simple and boring chess because that's what you like. If that's your kind of thing then fair enough. The problem is that you try to discourage and intimidate others into playing your style.
Yes endgame play does matter but opening play also matters. The endgame comes from the middlegame and the middlegame comes from the opening. You can't only separate the game into these parts as they are all connected. It's important to learn how to get an advantageous position from the opening and also how to convert it. Not one or the other.
searching a master DB to see what the top ( super GMs ) prefer makes little sense unfortunately. At the top only MLV consistently employs the Najdorf which you've established as the most respected.
But anyhow this discussion makes little sense, I'm sure with or without it you are fully capable of pasting lines that often do not make any sense for every opening that exists and also give recommendations on them.
I provided data on master level games. You don't provide data on anything and just cope by saying "Oh but they are not all super GMs so it doesn't count". You are not acknowledging all the other players.
The lines make perfect sense. There are reasons for each of the moves if you take the time to understand them. It's just your belief that people shouldn't bother taking the time to understand them.