Also, what got MS in trouble was their contracts with hardware vendors. Companies like Compaq were required to pay MS for a Windows license even on computers they sold without Windows installed, and that was an abuse of MS' power. If Google is charging companies for Android even for phone they sell without Android installed, that would be analogous.
[0] "While Android continues to grow its share of the global smartphone market, it is actually losing share in the U.S. Kantar’s data shows Android phones making up 55 percent of U.S. smartphone sales compared with more than 60 percent in the same period a year ago." http://www.recode.net/2017/1/11/14239038/iphone-apple-androi...
And yeah, sure, you could run OS/2 or even BeOS, but these never reached statistically significant penetration.
Just as today you can run Sailfish, or Cyanogen/Lineage, etc... the latter supposedly has a market share of 3% or so. Better than BeOS, Linux, etc... in 2001.
In 2001 if you wanted to switch off Windows you could buy BeOS, Linux, or OS2 and run it on the same computer that you had windows on. Back then I did just that, switching from Windows to BeOS when BeOS was made free, I did my university work on BeOS running on a Toshiba laptop that came with Windows.
Right now if you have an iPhone or Android phone you have very little option to switch operating system on your device.