We see Darth Maul and even Darth Tyrannus and see such energy. Then we look at the original trilogy and see Darth Vader usually just standing around, choking people with his mind. I think a number of people see Palpatine’s old apprentices and just think Vader is a weak addition, especially one who’s supposed to be more powerful than both Vader’s predecessors. Well other than the obvious fact he is alot slower and weaker due to walking on prosthetic legs in an iron lung where he can’t even eat solid food anymore, you have to understand Darth Vader is the ultimate darkness. It’s the darkness of the mind.
The fact that Vader is so quiet all the time, now knowing his history, should intimidate you. Everything he could have been, and he’s just sitting still, he hides his anger so it comes at you in the dark. It’s the most effective and terrifying rage: the anger you cannot see. His mask hides it; his introversion hides it. It takes the corpses of many Imperial Admirals/Lieutenants for people to fear him. And some didn’t even know what caused it (completely). Darth Vader was absolutely terrifying to work with. When he would walk by you, an irrational fear of being killed with his mind for no reason would strike into these men’s hearts and surge with the sting of electric shock. And I mean, that’s just him walking by.
He never spoke unless he needed to. You couldn’t see his face. And he had a severely short temper and an anger problem. Add his strength with the Force that didn’t diminish with his body and you have someone that makes Darth Maul look like impulsive, quick anger and Tyrannus look like a power hungry old man. Vader was the fear.