To your first 2 points: Yes, it's quite possible that some features shouldn't be implemented, and yes, it's unlikely that there is a simple rule to describe all the cases where things should and shouldn't be implemented. But that doesn't mean that they're not drawing the line in the wrong place now; it seems like you're arguing that because something is subjective it's irrelevant.

>> It... Literally does?

> I looked it up on Can I Use. It was for desktop versions.

I answered that after literally clicking the menu item and making sure it worked on my phone. My guess, after reading through https://caniuse.com/web-app-manifest , is that maybe there's something about service workers or background processing that they're not doing, but just sticking an icon on the homescreen, empirically, works fine.