> Correction, all of mobile users use Safari on iOS today. Webkit is your only option
When browser stats show X amount of people using Mobile Safari, those people are using Mobile Safari. Not a different web browser using WebKit.
> everything else is just the same browser with a new interface added to it.
There is more to a web browser than just its rendering engine. Chrome wasn’t “just Safari” up until they forked Blink. It used WebKit, sure, but it also had loads of development put in elsewhere.
Saying that an alternative web browser is “just Safari” because it uses WebKit is like the Hacker News cliché “I could do that in a weekend”. Sure, you might be able to knock out a proof of concept easily, but you are vastly underestimating the amount of work involved in the real product.