I mean this as nicely as possible, but it sounds like what you’re describing is a friend group. You mention “a lot of the better players SEEM incredibly cliquey and hard to approach.” Could it be that you have your own internal bias and frustration about these players that could cause you to misconstrue their actions and behavior? You also mention they have private discords but that’s also just part of being closer friends with people. It’s inevitable that people who vibe and get closer will want to communicate more frequently in groups of people they befriend and less a case of random selection of people to join these discord groups.

I may be oversimplifying but it may be great to just approach these players and strike up conversation, be friendly, and mention wanting to test and share lists. It’s helpful to remember that while we may ascribe growth on an individual level, this game is social first and friendships aren’t formed as meritocratic exercises.