1. Yes and no. Discord "guilds" have their metadata and chat messages managed by a single shard somewhere in GCP. However, voice is managed using servers hosted by ID3, a much smaller provider. If you find the right websocket server you can repeatedly take down voice instances still.
2. Emojis are just lines in a database, and yet they still charge a fee for that. The reason why it's free is because that's the selling point. Also, that sharded "guild" is actually part of a sharded container that still has a cost to run, and manages the write-lock for the data in that "gimme".
The whole tangent here feels weird since I _choose_ what to run on "my" VPS. Noisy neighbors have been a solved problem for decades.
3. This is actually the killer feature, centralization sells because of network effects. You're only on Discord because your friends are on Discord.
4. Teamspeak has this with myTeamspeak now. You've been able to have multiple sessions for a long time, but now it's in a nicer interface.
If you want to run a community with SUPER easy access to everything from live video chats with a hundred members to forums, excellent access controls, integrations for absolutely anything especially if you also use bots from the marketplace, Discord is there and it's free, and it always works.
It's really rough to compete with that.