Quite simple, water curing does the same as air curing, just much much more of a "curing effect"i've never understood the water cure method.. i know what it is but i dislike the idea.
Curing is the removal of all the salts and crap that are contained in the leaf, when you air cure, you don't remove as much of that crap, but enough so its nice and has flavor
When you water cure, you can water cure for 3 days for example, air dry it, and have some cured bud with some flavor after air drying, but speeding up the curing method drastically, or go the full 7 days and remove ALL the crap in the plant leaving the cell structures, and thc.
Thats what I have come to understand of it all, and the water cure works fine, and I always just want the cleanest, purest, and smoothest smoke possible.