> Slack, by far, is the best collab tool

I don't think any of them can be designated the best collab tool because they all (Skype, Zoom, Teams, Slack) have their strengths and weaknesses. I think Teams handles calls and video conferencing better than Slack, but Slack has a more intuitive and feature-rich experience for text-based communication and water-cooler style casual channels. Teams performs better on my machine. Slack has a much more reliable mobile tier. Zoom (not taking privacy issues into consideration) is unbeatable IMO for video reliability, I've used it for years across two major corporations now and it's yet to fail. I think Microsoft is aiming to make Teams unify the best of all these worlds.