Is the mapping from config -> state reproducible? Traditional distros drift over time with lots of upgrades because the state is not just a pure function of the set of packages to be installed (the "config"). It could depend on the system's history, such what packages were installed or removed in the past.

The so-called "atomic" distros don't attempt to make the (config -> state) transformation reproducible but rather sidestep the problem by snapshotting and replicating the output of the transformation -- the files on disk after various installs, upgrades, and config changes.