Being able to change your default apps has nothing to do with privacy and everything to do with platform control.
When tracked through apps, Google is equally open. Apple tries its best to combat tracking, but most apps will still do their best to jump through the tracking contention measures.
https://9to5mac.com/2019/02/07/app-screen-record-apps-remove...
I'd say, always be vigilant of the apps you install. I often check my http request logs to see my phone activity.
I suggest you have a closer look at the MicroG website where this is explained, too: https://microg.org/
The problema Is if you stick with Apple hardware there is no OS alternative
you're stuck with what the dictator (benevolent or not) decides