Michael, you are right as far as you go. I go another step and say that the zone system is not necessary with a neg-pos system, and that is the crux of the matter.
As an example, with a film with a straight line H&D curve except for toe and shoulder, due to the latitude of the paper itself, any exposure on the straight line can be printed on the paper with the correct adjustment for density and the zone is unimportant.
If you insist on using the film toe or shoulder, then zones may be useful, but you lose so much information that it is best to stay on the straight line of the negative.
The quality of the print is brought out by using the correct paper contrast and by dodging and burning if needed, and the correct film quality is gotten by correct development.