Probably better cause I'm pretty sure Vader doesn't have anything noteworthy of blades before ANH, I mean I suppose from accolades, but those only go so far(unless everyone is just assuming that Vader's skill has just been the same from pre-ANH to ROTJ). All of his saber feats thus far seem to be taking place after.
He's stated to be more powerful then he was as Anakin and we know that he was capable of stalemating Dooku in Dark Disciple regardless of whether the novelization is canon.
He's also hinted at being the most technically skilled Sith duelist in canon in various sources and its logical he would have grown in power up to Rebels where it's stated he's in his prime.