but the main point was that players ultimately decide the one "right" way to play and discard almost everything else as inferior or incorrect,
The "right" way to play the game isn't decided by players, it's decided by game designers and math.
there is always a more "optimized" way to play any stat based game. Stats and game mechanics are just numbers interacting with each others. So there are always going be one particular choice of actions that produces bigger number than other actions. Choosing the actions that potentially leads to the highest number achievable is called optimization.
And in MMO genre particularly, dev will try to create the hardest content that requires optimized strategy to beat so they can keep players busy and not quit after they beat everything. And that hardest content's number requirement is often very high.
For example, if the highest possible DPS achievable using the best in game choice is 100, then dev will design the hardest content by requiring 97 or 98 DPS to beat. Which means any other action choice that couldn't reach this number will be seen as inferior.
This is because the content design rewards stats optimization, by giving players unique rewards or accomplishments when they accomplished optimized choice.
And then of course this creates "social hierarchy" within the community that there are people who can play optimally and get rewards, and people who can't.
Ultimately the reason why these even happen is because game design rewards optimized gameplay by giving optimized players rewards. Game design is all about using rewards to guide player actions, so if you receive rewards by optimizing stats, then optimizing stats will be seen as "the right way" because rewards is given.
and everything related to the game not inside the game itself reflects and reinforces this (forums, guides, videos, addon
Even single player games are like that too. If you go to any single player game forum, people really only talk about 2 things: story/lore related stuff/fan art, or strategy to beat the game. Really what else can you talk about for a game?
In MMO forums people gravitate towards talking about strategy more because if the MMO is out for decades, people will run out of other topics. So what's left to talk about is really just strategy to beat hard content since it's often the only part that still keep people engaged after decades.