That strikes me as a frivolous concern, but if it worries Apple, there's an easy solution—add a "defaults" menu in Settings, like every other OS. Set it up so the default can only be changed by the user, and remains associated with the first party app even on uninstall.

We're coming up on the 13th version of iOS, and Apple hasn't done this yet. I don't think it's because they haven't gotten around to it.

Actually, I suspect that advantaging their own apps is a key part of Apple's business strategy for the future. Consider their recent shift towards "services". If the iPhone didn't exist, it would be silly to expect Apple to outdo major incumbents like Spotify, Netflix, and Venmo, but Apple thinks it can leverage its status as iPhone platform holder against competitors.

This becomes a vicious self-justifying cycle that is profitable for Apple but harmful to those consumers, who are kept tech illiterate when they're denied the opportunity to step outside their comfort zone and learn something new.