I think you missed the core of my argument there. Again, if the only reason people are using your browser is because they are forced to, you're doing something

I think you missed the core of my argument there. Again, if the only reason people are using your browser is because they are forced to, you're doing something wrong. Just because Chrome or Firefox could use their own rendering engine, doesn't mean the majority of iPhone users would switch to it. People who use Safari today would continue to use it even if Chrome/Firefox could switch their rendering engine.