I was making the argument that you made an assumption that didnt hold any weight.
regarding doing what slack can do, I think we do have a bit of collective amnesia about what was truly good and truly bad about what came before.
Slack does a lot of things, but its UX is actually pretty piss poor due to the bolt-ons (threads is just about the worst implementation I have ever seen), walled garden, weird account things (magic links~ if you want to see your other workspaces make sure you use the same email everywhere!), security (goodbye decent realtime bot api) and the client which feels slow despite using more resources than it should given its status as a program that needs to always be running.
To take one example of a worse system: IRC scales to tens of thousands of users on a single machine; doesn't have emoji or picture sharing though- but the bot API is simpler for sure, you can connect in one click if the person has an IRC client (or you pass a webirc link) - no signup needed.
I think the problem with slack is exacerbated in europe (or rest of the world in general), where the latency of fetching thousands of tiny assets or chats is many-many times higher than in California.
Also; the reason I had to do that was because my mum wouldn't permit a home internet connection; broadband was a thing at the time. Dial-up was not mandatory in 2002. IRC with dial-up was faster than slack is today too; you can argue that slack “does more” though.