Teams chat better than slack? Are we using the same Teams? Because it doesn't come close in my opinion, and the opinion of basically everyone I work with.
Frankly most of these tools have been at feature parity since before Covid.
At the end of the day, just about every team that I worked with had a WhatsApp group that they actually used to chat in. Having a bad product as your internal chat is how you get shadow IT like WhatsApp where people are discussing your proprietary information on a third party service.