Many parent control apps are more like Spyware and are often also exactly that, Spyware which spy on your Kids. Or Google Family Link is also a great example which you can’t remove even if you want too (as parent). I already setup a non-child-friendly blocking DNS and set the Age Limit in the Google Play Store and did all the Privacy related stuff, but I’m still thinking how can I make a Android phone more secure for children? The threads I’m talking about are non-child-friendly content, malware, scams, etc.
We’re talking out of the box solutions; what you’re talking about is custom roms that will be above most people’s skill set and time to do so.
iPhones are a thing because they simply work - that is a much bigger selling point than anything else you and I could suggest.
You have a point there.