No it's not? Android has upwards of 70% of the mobile market[0], and Chrome has nearly 65% of the mobile browser market, compared to Safari with under 25%.[1]
> the only choice any iphone users have
Sort of. WebKit is the only choice iOS users have, but there are plenty of browsers available on iOS (including Chrome and Firefox) that use WebKit, not just Safari.
[0]https://gs.statcounter.com/os-market-share/mobile/worldwide
[1]https://gs.statcounter.com/browser-market-share/mobile/world...