At work we've had both Skype for Business and Teams running in parallel with the freedom to use what we like. I prefer Teams to the point where I don't even turn on Skype anymore.
The other thing is that people can’t communicate between teams and Skype in many scenarios. There are also potential compliance gotchas for some scenarios that are difficult to identify.
I’m wary of anything new with Microsoft as when you stray from the happy path, (which changes over time) they don’t test or fix regressions anymore and create downstream problems.