It is one of those hard to explain or communicate well to others topics. People called Arnold's routine as too much, training twice a day 6 days a week. But who to say that once a day 5 days a week is not as demanding? it is up to interpretation and people's ego. People argue "I only need 2 days to recover" and "I don't feel I am overtraining".
Training for size and definition is like wanting to gain muscle and lose fat. It will work for a while, but then your gains will suffer.
You need to get very strong and you will get bigger. Trying to define 18" arms is easier and faster than trying to gain 2" defined. Not that I totally understand what the difference is, if you bench heavy, your triceps will grow..etc.
But that is the point behind abbreviated training such as 5x5, the 20 rep squats, etc. Concentrate on the 3 main lifts plus few hand picked extras and do them till you get very strong at them. When you are in new weight territory, you can modify your routine to shape, cut, or do what you like but at least you will have the strength to do it.
As far as the advanced training and why you may not be experienced enough to do it, I will only speculate the following. As you get stronger, you start reaching limits on your lifts. You cannot constantly add 10lbs a year, let alone a month to your lifts.
Once you hit such advanced training, the training becomes very demanding and very difficult with high potential of overtraining.
If your gains stop on the advanced routine, what would your recourse be? add more workouts, sets, or reps? reduce them? get rid of aux. lifts for the sake of the primary ones? drop the weights on some of the workouts and add to the lagging one? add more rest time? sleep more? take more days off? take a week off?
With the high potential of overtraining and because of the demanding nature of those lifts, you probably can still make comparable gains using easier routines for now.
Hope this helps.
