I agree, I always found it strange that an app aimed for gaming really has better performance than slack/teams and their massive budgets behind them. But I never saw a company that uses discord for communication.
Makes sense to me, its users would be running games alongside the software, and would be quite cross with the software shitting itself in the middle of a co-op game. Somewhat good performance and behaviour is (or at least was originally) absolutely necessary to getting traction, a bunch of checkboxes would not suffice.
Currently working at a place where at least one, if not two, teams use Discord for daily chatting. Official meetings are mostly handled over Zoom but I believe their intra-team stuff tends to happen over Discord.
Whereas Slack is successful because it understood it's usecase well (including how to sell to enterprises).