Has someone perhaps tried making a browser on iOS while sandboxed (aka. without JIT, and only sideloadable of course)? My understanding is that interpreted JS execution has abysmal performance and battery life characteristics, and given that Apple only entrusts themselves to run arbitrary code (since third-parties could just RCE themselves any bypass app store review otherwise) they can't allow other browser engines to use the JIT entitlement - it would look like they were intentionally handicapping the performance of other browsers.