Googles/Apples argument would have been much stronger if their stores managed to not allow scams/malware/bad apps to their store but this is not the case. They want to have the full control without having the full responsibility. It's just powergrab.
Scam apps are rife in the iOS App Store. But what they can’t do easily install viruses that affect anything out of its sandbox, keyloggers, etc
Is that really your answer? To make the phone ecosystem as fraught as Windows PCs for the average user? How is they worked out for PC users since the 80s?
Just to be clear, are you claiming that we would be better off if PC hardware and OS vendors had the level of control that smartphone vendors do today?
You really can’t trust developers to do the right thing - even major developers like Zoom (the secret web server) , Facebook (the VPN that trashed usage actoss apps on iOS) and Google (convincing consumers to install corporate certificates to track usages on iOS).
Even more to the point, you read about some app installed outside of the Google Play store that’s malware - including the official side loaded version of FortNite…
https://blog.checkpoint.com/research/fortnite-vulnerability-...
You really can’t trust developers to do the right thing
Indeed not, and that includes OS developers. Imagine if Microsoft had been able to block web browsers other than IE in the name of "security".