> What this does do is reveal the fiction that "iPadOS" and "iOS" are separate. Clearly not.

Technically, I don’t think anybody ever claimed they were 100% distinct. Apple, for instance, says (https://developer.apple.com/ipados/get-started/): “Powered by the iOS SDK, your iPadOS apps”, and they’ve touted the ability to build apps that ru on both iPhone and iPad.

marketing-wise, they clearly are separate, in the same sense as https://en.wikipedia.org/wiki/Car_platform: “A car platform is a shared set of common design, engineering, and production efforts, as well as major components, over a number of outwardly distinct models and even types of cars, often from different, but somewhat related, marques.”

The only difference is that here, Apple apparently ships all or major parts of the special parts for the iPad on iOS, too. Maybe they also do that vice versa? Can you enable the calculator app on iPad with this method?

They call it a different name. They want you to think those are two distinct things. They barely are. It's all to ensure that the EU doesn't get it's grabby fingers onto iPads too, as they don't have a big enough market to be forced to open up the app store. Please don't labor for free to improve the PR of a billion dollar company :)

Yet somehow some "tech journalists" are branding this as "how to flash iPadOS onto an iPhone". As you said, it's obvious that both iOS and iPadOS are compiled from the same source tree with different features levels enabled. The difference is purely marketing.