It's not like someone else couldn't have told him how to diet you know, someone from all the gyms he trained in, of all the pros he trained with etc.
You make it sound like if Arnold hadn't met Vince who was apparently the one and only font of knowledge at the time he would have been spinning his big fat wheels to this very day shaking his big jowls and scratching his head while pondering the eternal riddle of dieting that he never learnt because Vince died and took the info to his grave.
Weider sent Schwarzenegger to the best by sending him to Gironda. It was for everything-diet, training, etc. Joe knew exactly what he was doing. Vince putting the perennially arrogant Arnold in his place was part of it too.
As far as his personality, I have no problem with it, he was a purist. His personality was no more obnoxious than Schwarzenegger's actually lol none of the Arnold ball-washers realize it.
Sharma's wrong on Schwarzie's tris though, it's a common misperception. Both he and Coleman had good size, lacking only the sharp cuts needed to stand out against outrageous biceps in both cases.