However, antitrust doesn't (and shouldn't) protect you from competition. Too often I see companies just do a really bad job and the leadership just sits there collecting a paycheck and complaining to Congress about [big bad company].
Yelp is the poster child for this. Arguably even Mozilla is guilty of this [1].
DDG ultimately is just repackaged Bing search results. Bing itself lags behind Google and has the resources of a trillion dollar company behind it. It's not just a question of how much money you have but how you spend it. Look at Blue Origin. Look at the Metaverse.
So DDG's upper bound seems to be however good Bing is and honestly Bing isn't that good. What is their path to improving? I'm not sure they have one. But I don't think Google's relationship with Apple is the core problem.
Back in the day, Microsoft got in trouble (rightly) for bundling the browser. That's because the barrier to installing a new browser was quite high. Here phone manufacturers give you a dropdown to change it (which I think they should be required to do, as they are).
Antitrust won't solve poor execution.