I personally prefer Gsuite + Slack. But I've been on that "stack" for 15 years (although I also still use excel). Hard to say if it's better, because someone coming from the 15 years in the Microsoft world may prefer that.

One anecdote -- I just recently left a large, public company (that acquired the startup I worked for) and they were in the process of evaluating a move to Microsoft (to the point that they migrated some teams over). They opted not to make the switch and there were a lot of complaints from the testing group.

For a 40 person startup, I think two ways about it:

First, I cannot imagine this is the biggest priority right now. Presumably you're trying to hit some growth target. Is this really the thing holding you back? If you're in survival mode, this feels a lot like moving the deck chairs around on the Titanic.

But Second, if you're gonna do it, it's going to be a heck of a lot easier to do it at 40 people than at 60, or 80, or 100.

Overall, I wouldn't recommend doing it unless the ROI looks really, really good. If I was an investor or advisor it would drive me up the wall to hear that this is what you're distracting yourself with right now. And it's one of those problems that when you hit $MILESTONE, you'll have the money/team in place to handle making the migration go smoothly.