Couple of things though...
Anakin was a Jedi Knight in Revenge of the Sith and Obi-Wan a Jedi Master. However Anakin, if he was favored by the Jedi Council, would have probably already been a Jedi Master.
While Darth Vader was older and more cautious than Anakin, Anakin lost a lot of his Force power and potential after the battle with Obi-Wan due to the Force tending to require human bodies. While General Grievous was part robot, and had some enhanced physical abilities, he also had a beating heart etc. But he was less powerful than someone like Dooku. If he wasn't, Obi-Wan probably couldn't have outmatched him. When Obi-Wan lost to Darth Vader, it was part of the Qui-Gon Jinn plan to be immortal that was taught to Yoda and then Obi-Wan, and Obi-Wan disappeared, becoming I guess "one with the Force" to help Luke.
Another indication that Darth Vader wasn't that strong was that Luke beat him. And it goes with the theory that Darth Vader already being handicapped, Yoda and Obi-Wan plotted the whole thing with Luke or Leia overthrowing the Empire and maybe even the stuff about Vader
Now there was a scene in Rogue One where Darth Vader looked incredibly powerful. But the context was that he was fighting his very best and fighting wildly because otherwise the Rebels would get the Death Star plans
But is Darth Vader more powerful than Anakin? Maybe. Though I think Sidious and Yoda were higher level Force users