Nix is exceptionally good at making docker containers.
Want to throw a requirements.txt in there? No no, why would you even ask that? Meanwhile docker says yeah sure just run pip install, why should I care?
Like all LLM boosters, you've ignored the fact that the largest time sink in many kinds of software is not initial development, but perpetual maintenance.
If you care about getting it to work with minimal effort right now more thar about it being sustainable later, then sure.
Most of the complaints I've seen about Nix about around documentation, so "once you learn it" might be the larger issue.
In Spack [1] we do one layer per package; it's appealing, but I never checked if besides the layer limit it's actually bad for performance when doing filesystem operations.
tl;dr it will put one package per layer as much as possible, and compress everything else into the final layer. It uses the dependency graph to implement a reasonable heuristic for what is fine grained and what get combined.
The layer layout is just a json file so it can be post processed w/o issue before passing to the nix docker builders