Unfortunately I think Microsoft will definitely eat most of their lunch. Teams is so easy to set up for large companies, comes more-or-less free, and is super secure. IT depts won't take a chance on Slack or even actively move away from Slack to Teams.
Also, Slack has received a lot of criticism for their pricing strategy lately.
All this combined will make it hard for them to compete imo
Slack also benefitted massively from Covid. This graph is a good representation of that: https://www.statista.com/chart/22859/paid-customers-of-slack/
Unfortunately I think Microsoft will definitely eat most of their lunch. Teams is so easy to set up for large companies, comes more-or-less free, and is super secure. IT depts won't take a chance on Slack or even actively move away from Slack to Teams.
Also, Slack has received a lot of criticism for their pricing strategy lately.
All this combined will make it hard for them to compete imo