I think this would be the best solution.

Apples only (real) reason for forbidding sideloading is because then they could no longer force people to use their payments.

If developers were free to use 3rd party payment solutions, then Apple would probably be a lot more lenient towards side loading apps.

I believe that Apple generally wants to build what's best for their customers, except when money is on the line.

I think security is a valid consideration as well. The average non-technical iPhone user would not be hard to hoodwink into installing a 3rd party App Store full of malware. Agree, revenue is probably the primary driver.

The (real) reason to forbid sideloading is that it opens your customers up to the malware sewer that is Android. If sideloading is allowed it would take about 30 seconds for Facebook to create their own 'store' where the only product is Facebook apps with tracking turned on and data pilfering turned up to 11. You would see similar fly-by-night 'malware r' us' stores pop up pushing casinos, lotteries, and whatever other crap they can A/B test which shows that users with few technical skills can be tricked into using/installing.

Happy to have 3rd party payment options as long as it prevents sideloading.

The security on iOS comes from extremely well working sandboxing, not from Apple's control.

A lot of scam apps get through app review. From a security point of view app review is not effective at all.

That's just a story Apple likes to tell to hide the fact that they want the power to block anything they don't like.

The malware on Android is mostly FUD. But if the OS would be competent enough then this would not be a problem.

OSX is not locked and there are not millions of daily victims, so maybe it is not impossible to have low malware problems and freedom.