Each distro has it's own way of installing the drivers, Mint uses a driver Manager GUI, endeavour OS uses the nvidia-inst script, but ultimately, they come the repositories of the distro.
I've used it on Endeavour for about a year and on Tumbleweed for eight years before that with no real problems other than plasma-shell occasionally restarting. I have Nvidia and the open drivers.
When I'm in bed, Percy comes into the bedroom (he can open the door) and on to the bed. Then he proceeds to thump me in the head until I lift the covers for him to snuggle under them with me. Is that cute? I think so.
So I suppose you never use a browser to run a web application on the desktop :thinking_face: Anyway it;s a client server architecture designed for remote installation on servers as well as local installations. It makes sense to have one installer do both.
As to the old installer, when you knew about the un-obvious features, it was brilliant from a user perspective, but I'm willing to bet that from a developer perspective, it was hard to maintain, hard to add new features to, and fragile.
That's kind of like asking why we're not all driving Ford Model T cars, after all you could drive in them just fine. Technology moves on, best practice moves on, Hell, everything moves on.
A quick glance at the Agama repository suggests that the server is written in rust and the front end in react. I've no idea how it all works in practice as I don't use Tumbleweed any more. I really liked the yast installer but it was getting old.
I've had a brief look around and it seems fine for me.