I've used Discord for gaming related purposes on another computer, but it didn't feel... "better" to me. Sluggish at times, but in understandably large rooms with lots of traffic.
I'm mainly curious in your statement as to how Discord performs compared to Slack, and if better, how they achieve "better".
With Slack you need for every chat a new login/password and 100 clicks for sign-up, skip tutorial and email-verification, WTH why? Getting users into Discord is one single click. With Discord you have one login and you can have different names per server.
And Slacks admin pages are just a confusing pile of mess, my .vimrc is light-weight compared. Slack is so overrated and people just use it because everybody does.
Discord has never been sluggish for me.
However, both are timewasters.
Sidenote, I use it because the integrations take a burden off of me. Ie, my CI might not have integrations for Discord. My CI has plugins, and do those have integrations for Discord too? Etcetc. Being the most popular is not always just due to "we use it because everyone does".
Personally, I dislike how expensive Slack is. I'm not sure if I prefer Slack over Discord or not, but even if I preferred Discord, I'd still choose Slack for the integrations that I don't have to write myself.
Yes and if not there is a Slack-compatible API, check Discord's API doc.
Just try Discord, takes one minute and will know yourself if you like it. It's not a behemoth like Slack.