FYI, antitrust laws prohibit conduct by a single firm that unreasonably restrains competition by creating or maintaining monopoly power. The distinction you wish to make does not exist. If Apple has vigorous competition, then there is no monopoly or antitrust.
Apple still has under 14% of global marketshare for personal computers. The issue can not be here, as Lenovo, HP and Dell all individually have more marketshare than Apple, and Windows hold's 75% of installs.
Apple recently reported they have finally breached 15% of global marketshare of the smartphone market. Apple was leading the market by 2021 for the first time, but their position has slipped past Samsung's marketshare, which is now nearly 22% of global marketshare
So it appears Apple has vigorous competition.
Unsatisfied AppStore developers can complain and sue all they want, maybe the courts will swing their way, maybe not. I think it is a hard sell, being that I can't successfully sue Dollar General for refusing to sell my better mouse trap. It isn't my store, nor is it it's own economic market, because the market it participates in is retail sales. It is the same with the AppStore, no matter how popular Apple devices become, the AppStore itself is not an economic market; the market is software, and no one can say Apple is dominating the software market.
So, as a perceptive commenter above posted, The DoJ investigation is a big nothingburger, because the accusation of antitrust is invalid on its face because Apple is not the dominant seller in any of the markets it participates in, thus Apple can not be a monopoly, and since Apple is not a monopoly, Apple can not use monopoly power to unreasonably restrain competition.