Quickstart is way shorter, of course, and I mean the total for a homeserver and a bridge together. Reference documentation for the bridge configuration, often more detailed than minimally necessary (which is actually good) is of course longer. Lack of such documentation for Nixpkgs lib makes Nixpkgs manual shorter, but does not make Nixpkgs simpler.
Matrix is complex. It also achieves things email doesn’t fully achieve and nothing else tries. Still could be less inefficient.
But citing the length of reference documentation of some component as if it was the expected length of configuration is not a good argument for any claim, not even for a true one.