>The idea is to have multiple strong layers, not a hundred half-measures that are all easily bypassed

Definitely. On the other hand, in my opinion, "not running arbitrary code during package install" is not a "half-measure", it's a basic sanity. This whole arbitrary code execution at install time is a convenience feature that was adapted by some package managers, but it was never a good idea.

Fortunately, nixos solves that for me in most cases.