we were using slack and at the same time we had a subscription with office 365. after a while we hit the slack free limitation quota. and it got annoying. the search ability was useless in free tier. and more annoying whenever you search, it opens a webpage and doesn't do it in the app.
on mobile there were many cases that I didn't get notification of important discussions. rooms was the way to separate a talk. but it become tedious. each time for a new subject that you wanted to discuss, you needed to add all the team members into a new room. and after a while the room goes silent. you will end up with a tons of not-in-use rooms that you don't want to clean up them for history purposes. also the slack UI for sub discussion is very stupid. if someone forget to check the checkbox to post the subdiscussion in the main discussion thread, other team members even won't notice such discussion is in progress.
we was paying for office 365 and thought why not give the teams a shot. we won't be in worth situation than we are. we moved to teams and we loved it instantly, we had a separate tab aggregated all the files upload. we could reply on other talk. no need of creating a new room. this way room belongs to a team and not a certain topic. our sub discussion was visible to the whole team. enjoyed integration with azure and unlimited history. the best part was integration with outlook. it was a full suit solution. our stats become busy on outlook meeting events. we get weekly analyse. we didn't need to host our wiki seperated. we've created wiki per team. the communication was much more fun.