All I see is "there are no viruses because it's a small platform".
It's also a total lie. Do you know how many Linux servers there are in the world? It's a lot. Same for Android devices.
While these aren't quite the same, and thus not the same vulnerabilities as desktop Linux, they do provide some insights into the effectiveness of its security model.
240 million PCs were shipped last year, with about 10% being Apple. A negligible number run Linux. If we assume 5 years average life, that's still easily a billion active Windows devices.
That said, devices may not be the best metric. You mentioned users, which may use many devices. For instance, I use a Windows laptop at work, Windows desktop at home, Android on my phone.
I would use web server metrics, which are an approximate indicator of time spent on each OS.