Adding repos can just be done inside a Toolbox, or even as Overlays. Grub can also be edited and changes applied to immutable OS’s like Bazzite/Kinoite. I’d definitely say give it a shot on a non-daily driver machine and see how you like it. Having the option to mess with the underpinnings can be nice- but not having to has a lot of value as well.

I know, right? It’s so hard to “really” mess something up and Toolboxes are very cool for things not served by Flatpaks or Overlays.

Regarding your not wanting to go with an immutable distro: what configs are you thinking you’ll need to mess with that makes an immutable distro a bad idea exactly? I was previously on the fence about it as well but Bazzite has absolutely served my needs and requires way less fiddling than my previous Nobara install did after major updates. I have yet to find any day to day configurations that I haven’t been able to overcome with OSTree overlaying. Aside from being immutable, Bazzite literally checks every other box you’ve got listed.

Isn’t this almost the inverse argument to the android vs iPhone thing? Like the iPhone being (traditionally) more expensive for the “same technology from 5 years ago”? I don’t really have a horse in this race, I’m a firm believer in use what you like and is easiest/best for you. But I do feel compelled to call this one out a bit.