Yep i agree with that. Vader wasnt the perfect sith,by sith definition.But vader was the perfect hermaphrodite in the force. He knew both sides and never really desire control.
But after padame died,yes there was no more drive,until luke came in the picture,then vader felt even more sentimental towards life. No vader was a softy,a powerful one too. Just got tired of being told what to do,from obi wan to the emperor, he just got fed up with it.
Now some say galen would of been stronger,yet if he trained more he could have been. But no not even galen could stop vader,i still like galen i think he had more potential then vader,but vader was the choosen one,if only he stayed more on the light side. Yet he needed to fall to embrace both aspects of the force so he could be given the title choosen one. No jedi could have been as powerful as vader,at least in this saga.
So if lets say vader was given a "better" position he could have been more powerful then luke even,after all luke is child of vader.