Exactly. First, the fight is controlled by Vader. Ashoka runs at him for the first swing, and again when he's focused on Ezra, otherwise it's Vader who controls and is the aggressor. Ahsoka is basically trying to survive, not win. This episode is the best fight we've ever seen between Vader and someone remotely close to his skill and power level, in any media. Only the Kenobi fight in Episode III compares. The New Hope fight was weak, in Empire he was holding back because he didn't want to kill Luke, and in Jedi his heart wasn't in it. This was Vader as we've always imagined him and wanted to see. Ahsoka did very well, but she was never going to win unless Anakin resurfaced.
The entire point of Vader is that he's the baddest of the bad. There's a reason he's considered the top screen villain in history. No one can beat him unless he allows it. Even the Emperor knew Vader was more powerful than he was. The Emperor is only on top because of skillful manipulation. You can't undermine that characterization by having any one Jedi/Force wielder beat him, let alone someone who probably hasn't had to fight anyone with even basic Jedi skills in 15 years like Ahsoka. I'm sure Ahsoka could stand a chance against anyone else. This isn't to minimize how good she is. The point is that Vader cannot be beaten. You can survive him as Ezra and Kanan did the first time they fought, and as Ahsoka seems to have done here (although that is very open to debate as we don't really know what was going into that cave at the end) but that's it. Despite a good fight and a massive explosion, Vader walked away.