I think he'd be capable. Even though Vader wasn't as agile as his past self, he was still capable of stomping Ezra and Kanaan together, the latter of who was able to defeat the Grand Inquisitor with extreme difficulty, someone who was stated by the creators of Rebels to only be slightly weaker than Ventress, who was not only an extreme diff opponent for Padawan Anakin, but also for other high tiers like Anakin and Obi-Wan at their peaks. Along with that, even adding in a far stronger and experienced Jedi like Ashoka didn't do much to help the Rebels confront Vader, who RotJ should scale from in all aspects.
Don't see Padawan Anakin accomplishing the same against those 3 Jedi, even if he's more agile.