Most of the guys i think of as huge worked each muscle 2-3 times a week. Coleman, Oliva, Draper, Schwarzenegger, Scott, etc. 2 days on, 1 off, or a 2 or 3 day split, etc.
As far as the overtraining concept, the idea that this will overtax the CNS is just a theory, one born of HIT that few believe in by the way. The government and other similar sources have recently revised their exercise guidelines upwards, to more exercise on a daily basis, because of a believe that the body not only can handle it but benefits from it.
Intensity with moderate sets will not tax the CNS, i've done it for decades. Volume would be wearing, especially with any degree of intensity, because you're essentially doing the equivalent of marathon running. Wearing down the system with endurance work.
Once a week works for some but in each case i wonder what potential they've left on the table using it. Some believe as i do that after 3 days between workouts per muscle you're essentially sliding backwards due to disuse.