My biggest problem with Teams is that it doesn't deliver messages when it thinks the computer isn't active. Got Teams running on Computer A while you're working on Computer B? Don't expect to see anything from anyone, not even if you frequently glance over at your other monitor.

I got a mouse wiggler just so that I could get messages.

The most fundamental feature of a messaging platform is messaging. If it can't do that properly, which for some reason Teams can't or won't, then it deserves all the hate it gets.