Most apps on the list are lemmy apps, meaning they don't work with kbin. Artemis is specifically designed to work with kbin, not sure if or when any of the other ones will go in that direction or become interoperable as there are some challenges with the kbin API at the moment. Having said that, a new API is in the works so things should get better with time.
What would be a feature in any of those which would make it worth to use it instead of just installing the website as a webapp? I've never used any 3rd party apps for reddit either. Or is it just about it feeling more native on that platform?
Easily collapsible comments plus children , UI tweaks , accessibility enhancements, multi account support (with feed grouping) are some possibilities that people enjoyed on Reddit through 3P apps.
I have no problem running PWAs for things, but I'm not an enormous fan of the Lemmy default browser interface either. It's not terrible, but currently I think Jerboa is better than it (just), and I'm keen to see other developers improve further on it. Some of the Reddit third party apps were very polished and feature-rich (compared to both Reddit's first party apps, Lemmy's first party interface, and Jerboa), so something of that calibre would be gratefully received.
There's an argument to be made that (because of the structure of Lemmy) new interfaces could and should be integrated with the main codebase as themes rather than as genuine third party API consumers, but from an end-user perspective that doesn't really make a difference either way.