Well I think both Nix and Docker delegate the actual resolution of dependencies and it's not about implicit vs explicit dependency management, alone, it's more that with explicit dependency management you get reproducability.

And with reproducability you move the work from fixing broken builds, to implementing builds.

Of course, I can tag docker images and upload them to an internal registry, but that seems more complex to me, than doing this at the source level with Nix.

But 99% of the times that's exactly what you need.