I think Apple has also done good things with their strict app store policies (from my consumer point of view). Apple has been for example putting limits on data collection and tracking. The main mechanism is to kick apps out from Apps store if they don't play by the rules. I'm worried that side loading will be a step back here. Strong players, like Facebook, may just take their app away from the official store and di…
Looking at Android, where sideloading has been available forever, there doesn't seem any evidence of your worry.
It’s only worth it to app makers to have side loading if they can do it for large numbers of users, bypass the app store’s rules, and bypass apple’s take. I’m expecting apple to set it up in a way they can do none of those things, by making it cumbersome to sideload, not giving entitlements to apps not published through the store, and by taking a cut for sales from sideloaded apps.