iOS isn't particularly open source friendly, but mostly people don't do it because of personal incentives, not because it can't be done.
It's subjective, and I get that, but what you miss is that features are subjective too. Missing parity apps are only relevant when you care about that feature; at no point in my life have I ever thought my life would be better or more convenient if I could only torrent on my phone.
But having an app that is responsive and works well has made my life better. Standing outside a bar in the rain trying to get a stupid Covid app to work, not work well, just work, on Android has made my life worse.
(Ironically, I've kind of noticed this is part of the Unix ethos writ small: do one thing and do it well. It's not exact, and iOS for sure has tons of crud everything apps. And they sure don't work together! I just think it's amusing.)
I don't think iOS is less feature rich except in some specific areas, like web browsers, but you can see in the extreme example that if you could use any web browser for 20 minutes before running out of battery vs safari for hours, one is clearly better. Then you're just haggling over scale. Having the choice to use bad options is not really a choice, unless you have to eg for certain functionality.
And like, in other contexts this isn't even a debate. You talk about the useless feature bloat of Microsoft Word and the associated UI crud, and people are like 'yeah'. But in this context people will straight up make an argument that n+1 features better than n features.
How can whatsapp be better? Android at least has features like scoped storage.
Where is the ios equivalent of newpipe? Where is the iOS equivalent of pojavlauncher? where is the iOS equivalent of libretorrent or syncthing?
Open source is essentially banned on iOS.
What is the advantage of iOS? "Feels smoother"? Totally subjective.