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?
In the modern day, I actually think this mostly works? Are you aware of instances where normies installed Windows malware because they purposefully disabled Windows Defender?
Everyone always talks about the "Dancing Bunnies Problem" but I'm not convinced it's actually a thing.