Case in point - we use slack at work, but when we need a call we'll typically use discord instead, as slack is horrible for calls (blurry text when screen sharing, often doesn't always let everyone on the call, etc). If everyone in the company started using discord for text chat as well, there would be very little reason to stay on slack and keep paying, as it wouldn't be worth it. Slack don't have something like office 360 to keep companies interested if chat fails to deliver, so all of those customers could evaporate pretty quickly.