I like the traditional package system, I don't like containerising everything (though I know that is not necessarily coupled with immutable distros). Because then every package can have different library versions and the dynamic loader can't do its thing.
But it's more the configuration that I want to be able to adjust, or to recompile things. As a typical example, on alpine I always need to recompile sudo as their standard version doesn't allow PAM which I need. On an immutable system such tools would usually be in the immutable part.
I had problems with macOS when they switched to immutable (and if you turn off the protection it turns off a whole load of other things too). If I as much as changed the /etc/ssh/sshd_config it would revert with updates.
And really the traditional package system works totally fine for me.
I think you're taking the term "immutable" too literally.
Immutable does not mean you cannot change it according to your wishes. It just means that each change must be explicitly declared in order to be included in the next system image.
In some ways, having a declarative, immutable distribution makes the process even easier, as is the case with NixOS. If you want to patch your sudo, it would be as easy as doing
100% truth be told, having a declarative, immutable distro has allowed me to experiment and configure my system way more than I would have otherwise. I mean, I can do anything because I have the safety net of rolling back if I mess up.
Furthermore, being declarative means I know exactly how I got to my end solution, instead of having to memorize a bunch of steps from different attempts that may or may not have been successful.
Declarative is very different from immutable. They're two separate concepts.
See Apple's implementation where the OS files are protected by signatures and the system won't boot if they're changed. Immutable does mean you can't change it, though I'm some cases you can enable and disable some parts. Nix is declarative and perhaps not immutable. It's advised not to mess with config files but you still can if you wish, it's just a bad idea because it'll be overwritten.
I'm not really against declarative management though I'd consider it something more appropriate for servers where I don't want to change stuff on the fly. On my workstation I don't want to do a complete change time every time I want to modify something. I also don't want to learn the complex syntax so I've never really dived into nix.
I like FreeBSD's compromise of having most configuration in one file but still a traditional system.
But it's more the configuration that I want to be able to adjust, or to recompile things. As a typical example, on alpine I always need to recompile sudo as their standard version doesn't allow PAM which I need. On an immutable system such tools would usually be in the immutable part.
I had problems with macOS when they switched to immutable (and if you turn off the protection it turns off a whole load of other things too). If I as much as changed the /etc/ssh/sshd_config it would revert with updates.
And really the traditional package system works totally fine for me.