"They chose that route for a myriad of very significant reasons relating to user experience, usability, privacy, security, safety, brand & reputation, performance, and accountability."

This is incredibly naive.

They chose it to be this way for the purposes of profit.

Android is testament to the fact that high degree of quality and security and consistency can be maintained without any of the most iOS aggressive restrictions.

There is no material difference between security on either platform, they're both generally fine, apps are great on Android and people are not falling off the side of the earth because of 'scams or fallouts' regarding Android.

The existence and relative quality of the Android universe renders most of the arguments for iOS walled garden moot.

The term 'monopoly' may not apply perfect, but it's reasonable in the discussion, the anti-trust issues are obvious and have many historical parallels.