If I as a company say I’m not interested in Teams and want to not pay for it as I do not plan to use it, msft will tell me it’s not possible.

This train of thought doesn’t work because the price didn’t increase when Teams was added to the bundle. You weren’t forced to pay for Teams because Teams was added at no extra charge.

Therefore, businesses like Slack can never succeed because I as a company will never look at alternatives if I already get a messaging app built into my Office suite.

That’s not how it works. Chrome succeeded, didn’t it? Firefox is still around, isn’t it?