Big Caveats: 1) I wish I could see the raw data also. 2) I’m totally second guessing my original analysis. 3) I haven’t looked at a lot of data on this subject in the last few years.
However, I doubt that Skype for Business is being used by 100% of IT pros at companies with 100–499 employees and 94% of companies with 500+. Of course, I really don’t see how an IT person could do their job without Skype — I hate it too, but I always get requests from overseas to use it.
I looked at this albeit biased study: https://www.skyhighnetworks.com/cloud-security-blog/7-charts-reveal-the-meteoric-rise-of-office-365/. It shows 91% of companies with 100+ employees are using Office 365. Among the same cohort, it reports that 60% use Skype for Business Online.