There's also some conflict of interest if say Chrome were to come to be the dominant browser on iOS since they also control Android. Would battery life, performance etc be prioritized as highly on iOS as their own platform?
I think it would be nice to be able to load apps from outside the app store especially on devices like the iPad Pro, but I think that's a separate issue from web standards. I think the only practical way to advance web standards is for the major browser vendors to agree and implement them, even if that sometimes takes a while.