> Doesn't Discord require every user to create a new account, even if they're already using Discord in some other community? So when they say "a Discord server", they really mean it--they're like droplets running independent deployments or whatever (albeit managed/hosted instances run by and upgraded by Discord the company); not like subreddits, right?

No, it works exactly like subreddits. One of the major lock-ins Discord has is that all the communities are there, and people access them all with one account and one app. It's very convenient, which, as RMS says, is a bad thing when it comes to proprietary software.