It`s going to show this is my first post, but far from it. Been around since 1996
As far as the marathon 12+ hour practice days, a lot of discussion is at hand. When I was at GIT we would have hands on our instrument easily 10+ hours a day. To the point that some of us discovered spraying Chloraseptic throat spray on our fingertips would numb them enough to keep playing.
Is it necessary? For some, yes. There are people out there who can build the technical facility to play very intricate things with comparatively little effort. Since this is in fact the VAI board, I will share something I got from Steve himself: Practice as much as you are compelled to. Not everyone has it in them to sit down and work on guitar for 12 hours a day. And most of those people can go on to become extremely proficient players.
I can say this; if you were to sit down and really focus (quality of any effort is how much you can focus on it) for three hours a day CONSISTENTLY, you could and would progress fairly swiftly. The magic to it is picking it up with the intent of spending three hours GETTING BETTER, not just playing the things you`re already comfortable with.