“One” is generic...but it’s not descriptive. In other words it’s not cloud, drive, OS, etc. So in the context of computer goods and services One could be trademarked (which of course MS has). It’s like saying Apple is generic, it is but as Apple relates to computers and software it receives trademark protections.

When MS uses “one” across its product spectrum (OneDrive, Xbox One, One OS, One Note, One Guide) then google uses One...it’s not the same as MS OneDrive and Google Drive (ie descriptive) it’s more on par with MS creating a social network and calling it MS+. I think most would agree that’s either a ripoff or at least fail on many levels.