I have close friends from a TF2 community server that's been dead for over a decade now, but I can't think of anyone I've met via random matchmaking since.
Game servers are the perfect digital third space, it starts off with random players but as you log in each night, you see more and more familiar faces pop up and before you know it you're all regulars popping in to chat while playing a few rounds, learning more about your new friends and praying to god that you've got the godlike Finnish sniper player on your team.
By comparison, modern matchmaking-lead multiplayer feels gentrified and - for lack of a better term - soulless. You're blindly shuffled between random players each game, and there's no way to properly build a connection with players or a community out of it. There's a vacuous and temporary nature to it all that just feels cold.
Edit: also the fact that things like skins & sprays - player controlled ways of expressing themselves - have been neatly packaged by gamedevs and sold back to players at a premium. It feels completely antithetical to the player-led nature of what such games used to be.
It's not a discord problem it's an online culture problem. People now are addicted to trying to find things to be upset about and put people on blast for - make an off coloured joke in the old days and you may suddenly find your new best friend, now it's being clipped and shared on twitter and some one is calling your boss to try and get you fired.
I'd go a couple of steps further, not the tools, or even the people, or even the culture, but rather the incentive structure. There are massive social rewards, psychological rewards, and even financial rewards, for identifying and sharing a novel source of outrage.
As you said, this produces a culture where there are steady pools of people both seeking out the content, and waiting to consume it. The flip side of this is that everyone also knows the game, and manages their online presence so they don't end up on the trending tab of twitter.
Pseudo Anonymity is sort of a key feature of IRC that I think acts like a strong filter for people
People who are jerks will use anonymity to be jerks whereas when they are forced to tie an account to their identity they might pretend to be not jerks
People who are kind when anonymous are likely just good people at their core
I made so many friends by joining a lobby and just playing a game for a few nights in a row or whatever
Now I don't know how to really connect with people online anymore or build any kind of community
Discord servers don't seem like the right way, they are too busy and chaotic for me
I miss making friends online and gaming with them