They are (IMO) correct that having less layers between you and the lowest layer is ideal. The browser is an engineering marvel but it’s still a nuisance to work around.
If you depend on, say, Qt-for-iOS, then you need Qt to integrate the new features (with more or less success, taking more or less time), and you have a much higher chance that Qt will stop working on iOS some day (or that some important feature never reaches Qt, or that it is super painful to use with iOS).
Removing third party dependencies reduces your risk.
I admit that I am not saddened by this hurdle. The moment that becomes a thing, further enshitification will ensue with every web site trying to drop and icon and start pushing messages.
“Closer to metal”? Not sure you are wrong to ask if there is a line given SwiftUI. That is some very high abstraction.
If you wrote pure machine code without system calls you can't even read a file. You have to call into the kernel, which could even be written in javascript, in order to do that.
