Here is the BOTTOM line....
Despite 50 years of the theory, HIT theory has failed to produce the promised results. HIT was tried by almost every gym rat in the 70s-80s because, lets face it, who doesn't want the same or better results with less time in the gym? Only problem is..it didn't work well for people.
Look at how the modern bodybuilders who are winning contests train...is it like HIT? or...higher volume? HVT only exists as an ex post facto..meaning, no ones goal is to train "high volume". That is simply what the optimal routine looks like for most people after the routine is planned out. I don't know one person who says "I'm going to do high volume just because..."
Effective routines just happen to look like "HVT" when all is said and done. Volume rules.