I'm an admin of both Slack and Teams. Almost all of this is due to how his org configured Teams. While there's some valid complaints, a lot of this comes down to IT not understanding the needs of their users or simply not caring about the needs of their users because of some stupid opaque management decisions. You can mute chats same as on Slack. You can be forced to autojoin same as in Slack. I have regular meetings with customers in Teams. While Slack is absolutely still better at what it does most of his horrible experience comes down to crappy settings by his IT. The mobile device integration is truly abysmal though. Hoping in apps requires you to install those apps as well to do simple things like project management. The whole point of hooking in an app is to not have to go directly to said app. We haven't had a problem with notifications either. Most of what's possible in locking down Teams is possible to do it Slack it's just not default.