Fun fact, the Google Chrome team was very aware of “browser chrome” as a term when they named their browser. They make that clear in the introductory comic.
Apple isn't the most dominant business on earth, so maybe they can't do anything in violation of antitrust?
Not how it works. You define a relevant market, and the market of iPhone users (which a stable market, there are barriers to just switching to android tomorrow) can be used for evaluation.
This really is a grey area. You can't define "the market for electricians in my local town" and get any antitrust protections. Defining the market is a huge part of how politicians make this political and therefore something they can profit from.