As someone who uses Discord, I can tell you it goes down too. My favorite part is looking at their status page, seeing that API response time is exceedingly high, and getting no updates from the team about whether or not they're fixing it.
I am on multiple OSS Discord servers with thousands of users, and it works just fine most of the time.
I am on multiple Slack servers with just 10-20 users and it is unbearably slow.
Server-side scaling was only an issue with OSS communities and for hackathons, where >50k people were online.
Slack has a more mainstream look and feel which is probably one of the reasons it's preferred by companies.
There's no way that my company would adopt a platform so "fun" in the way Discord tries to be. Animated characters, a logo which looks like a gamepad, etc...
It sucks, because I use Slack for work and mostly Discord for personal use (mostly dev communities for different companies), and Discord is far and away a better experience. If Discord provided a "cleaned-up" offering for orgs like mine (finance), I think it would be an instant hit.
https://techcrunch.com/2020/06/30/discord-now-has-a-3-5b-val...