I think discord is primarily just useful for voice chat, yes.
But:
It’s a closed ecosystem that locks what would otherwise be searchable knowledge on the web, with an unsearchable, proprietary lockdown of that information.
Yeah, no. Proprietary, sure, but you can say that about almost communication mechanism that’s not a website with an API. It’s not like people would otherwise be posting these things somewhere else if discord didn’t exist. If it wasn’t discord it’d be slack or something. Discord is an entirely different medium and complaining that it isn’t a forum is just not a legitimate argument. They’re entirely different things.
Well gee, I hope you don’t use texting, phone calls, emails, private forums, social media DMs, or talk to anyone IRL, because those aren’t searchable either!
This argument seems like reaching for something to complain about rather than having a legitimate problem with discord. If anything, you don’t like the “large group chat” paradigm, but that’s like hating a screwdriver because it’s not a hammer.