If they add sufficient warnings about sideloading etc. then I don't see a problem.
If your mom is incapable of listening to these warnings and follows some guide to install some walware then I'm sorry but maybe she needs parental controls enabled or just a nice talking to about how to use her phone? Forcing everyone else to lose out on game streaming or Spotify signups seems like an overreaction to the problem and an oversimplification of the solution space.
Uhm, I guess that's true in the same sense that it's usually more rainy in New York than Chicago: One click RCE aren't exactly impossible for IPhone, just historically more rare than on android. Though recently at least one exploit broker stopped accepting iOS Safari one click RCE because they just got too many shrug.
> "Popularity does not make you right" I'm not saying that the closed approach is fundamentally better than the open approach, but it sure is for some use-cases. That's why we have a phone OS duopoly.
Regarding Apple's garden walls not keeping all the creepy-crawlies out, sure, but it's vastly better than on Android.