Oh man, this is so much better than the Old Man Kenobi vs Old man Maul fight. Vader is using his anger in his fighting style, and Kenobi shows why he's the only surviving Jedi Master from the Old Republic. Yes, I do count Yoda out at this point and Ezra is in that weird place. But Ezra is completely different case altogether at this point and he cannot be counted as "the master."
Maybe I am starting to get why Ashoka didn't get Jedi Master badge at the end as the Jedi Council couldn't see that the universe around them was grumbling and they couldn't renew themselves. So, Ashoka was forced to find her own mastery, while Anakin turned evil, and when the Rebels ended, she was still in between practices, and I cannot say for certain that she was a master of anything. Other than survival.
If I compare Ashoka's fight to this, Anakin ... er, Vader has certainly developed his skills to even rival the best Republic could offer. And he had got more pissed, which is logical taken that Kenobi was the one that cast him in the world of pain. In Ashoka's fight, Vader was holding back.
In a way maybe he wanted Ashoka to win so that he could end his suffering.