GH is misunderstood, that is why some people think it's overrated. If you think GH is overrated, then you are expecting it to do things it does not do, because it does what it's supposed to do oh so well!
Number one: Anti-Catabolism. You can train with more intensity and more volume, you can hold more muscle while off or dieting. Dan Duchaine was right on the money about this one.
Number two: Connective Tissue Repair. This effects joint strength, tendon strength, etc. Remember the tendon decides how hard it ALLOWS the muscle to contract. This effect is so strong the current doping test for GH is connective tissue repair markers that are too high.
Number three: Lipid mobilization when insulin is quiet.
At no point should you expect GH to be anabolic except where it relates to one and two above. Long term size is about a lot more than just growth, it's about not losing muscle during catabolic times, and being able to lift hard and heavy as much as possible without joint stress or injury.
This is pure speculation, but I think if you took GH alone over a long period of time with healthy natural test production and proper eating, you would be a monster in the long, long run. I bet national level size with 15-20 years of training and perfect diet and good genetics.