NixOS has the best concept and even pioneered it, but whether its implementation and documentation is perfect is a topic for debate.
However, it's been quite long since I had to fiddle with my config and as such, the downsides don't really affect one on a daily basis. In fact, I recently reinstalled my machine to change the root filesystem and it was an absolute breeze. If not for secure boot, it would have been absolutely trivial, and with secure boot it was easy and convenient.
As such, I consider the pains an investment into system that runs much better down the road. Though I'd love it if these pains were reduced.
Yes! Apologies, didn't proofread what my phone produced from swiping