The problem isn't that one browser is dominant. The problem is when Apple develops a feature entirely in secret and then doesn't bring it to a standards body,

The problem isn't that one browser is dominant. The problem is when Apple develops a feature entirely in secret and then doesn't bring it to a standards body, forcing other browser vendors to reverse-engineer that feature. Apple is shipping those features, and evangelizing them to developers, before the other browser vendors can even get started reverse-engineering them (which they shouldn't even have to do in the first place). Now, you could argue that that's in Apple's interest, and you could argue that "it's their browser and they can do what they want with it". But you can't dispute the fact that they're not helping web standardization in the mobile space. Which is a problem for anyone who wants a more standardized web.