I don't think that's true at all. I've talked to a lot of people who wonder when Google will come out with Chrome for iOS. Now that it's out, it's marked 17+ (because it escapes Apple's filter), can't be set as "default browser" and I imagine that it doesn't use v8 (used to be against the developer agreement; possible doesn't even use Nitro).
Apple has technical limitations in place to prevent alternatives from being as good as the default. A simple example is setting the default browser/email application. I'm not sure if this is still true, but Apple had a policy preventing 3rd party browsers from being anything more than a skin over Safari.
Since Apple is in complete control of the App Store and there aren't any 3rd party app stores, Apple has no incentive to allow alternatives to it's default applications.
