No, they're not. And by saying that, you're proven why the "fight" will also result in the other side winning. Ignorant, pedantic, arrogant, and entitled technical people vs the rest.
Of course they are edge cases. How many people do you think install third-party apps on Android? Pretty sure hardly anyone does that.
Also, Windows works pretty well with software from third-party sources, or would you forbid them in Windows as well? Sure, there are the occasional crypto scams which disable a hospital here and there, but this can arguably be prevented by not giving non-admins admin permissions.
99.9% of scams on Android/iOS happen by making people install remote assistance apps from... the "100% safe" app stores. So, no, you're completely wrong.