Technically pages alternate between W and X as you say, but this will disable even that (which is already true AFAIK for non-Apple iOS apps, they can't have JITs).
They can’t have their own JIT. If you use SFSafariViewController or WKWebView you’re using Safari and it’s standard JIT. But you have no access to it outside normal JS so it’s no more exploitable than the Safari app would be.
