> Thus one cannot make a JIT compiler for js and thus pages are slow.

Lack of JIT doesn't slow down pages much. I believe the difference is so small that it might even be possible to be faster without JIT for most pages, especially on low power devices, it's only computation heavy pages that are going to suffer and even then it's not like you can't optimize common patterns statically ahead of time.

It doesn't mean that it's a good idea to invest into it, you are still under Apple's mercy and they clearly don't want competing browser engines.