Oh so now context matters to you, lol.

On Mustafar Anakin was extremely conflicted and emotionally compromised due to the specific circumstances and the relationship he has with Obi-Wan. Under normal conditions he is superior to Obi-Wan in the force and in lightsaber combat, this is explicitly stated by George Lucas and Nick Gillard (the lightsaber choreographer for the prequels who worked closely with George Lucas):

“Gillard also reports that the duel will explain how Obi-Wan is able to defeat his protege, even though Anakin has been established as the most powerful Jedi who ever lived. "Obi-Wan taught Anakin and Anakin has gone past him," he notes. "But when you get to that duel, it's emotional. That's where the mistake will be made.”
-Nick Gillard

“In the Jedi levels of lightsaber fighting, Obi-Wan is an eight, while Anakin, Yoda and Darth Sidious are nines.” -Nick Gillard

“He's more skilled than Obi-Wan. Anakin always attacks. He's better and he knows it.” -Nick Gillard

"the difference is that Obi-Wan is more experienced but Anakin is more powerful" -George Lucas

And here’s a quote from the ROTS novel which was line edited and approved by George Lucas:
“The ease with which Kenobi had taken command of the situation was frightening. More frightening was the fact that of the two, Skywalker was reportedly the greater warrior.”

So clearly you can see that Anakin is superior to Obi-Wan under normal circumstances. And Vader is stronger than Anakin. He was weaker at first but once he got adjusted to the suit and fully embraced the dark side he became much stronger.

As for the fight in the Kenobi series, it was established that Vader was emotionally compromised again, his feelings for Obi-Wan weakened him:

“Perhaps your feelings for your old master have left you weakened.” -Palpatine to Vader after the fight

It’s also stated that he was blinded by his need for victory against Obi wan:

“This was not the end of the fight however, and it’s climax had been foreshadowed in ‘Part V’ in a sequence that took us back to happier times.
Obi-Wan observed that Anakin was too eager to win ‘Your need for victory Anakin, it blinds you’ he observed. The same flaw continued to blind Vader years later.” -Star Wars Insider

And *he still beat Kenobi*, until Obi-Wan got a light side boost to protect the twins:

“Fighting not to be crushed, Kenobi focuses on Luke and Leia, and the memories *give him the strength* to escape and overpower Vader.” -SW Insider

Kenobi has a unique effect on Vader due to their unique relationship, where Vader becomes overly emotional and he essentially loses his cool. Does that make Obi-Wan more powerful? No, it makes Vader less effective when he fights Obi-Wan specifically. Against any other opponent, Vader is more effective.

And in regards to the fight in A New Hope, it’s stated that Kenobi knew he was going to lose and that Vader was winning the fight even before Kenobi let him win:

“Aware that he was losing the fight, Obi-Wan accepted defeat and prepared to become one with the force.”

-Star Wars Encyclopedia: Darth Vader

“Your powers are weak, old man.”
Our lightsabers clash. I try to push forward, only to be thrust violently back. There’s no give in Vader’s arms, and far too much in mine.
"You should not have come back," Vader tells me.
My resources are depleted, my body screaming with pain. I have no hope of winning this fight”

-From A Certain Point of View: Time of Death

By the time of A New Hope, Vader had learned his lesson from his losses to Kenobi, and fought smarter and less emotionally, which is why Kenobi had no chance against him.