Does WandaVision finally end a long-standing MCU debate? Possibly. Since forever, the audience, and even the characters within the MCU, have debated on who is the strongest Avenger. It all started as a game in Avengers: Age of Ultron, when the team tried lifting Thor's hammer to prove their worthiness. It was then believed that anyone worthy enough to hold the power to rule an outer-space realm of Gods should be the most powerful, thus, making Thor take the number one spot. But, in that film itself, Vision lifted the hammer-like nothing, and threw that false belief out the window. Of course, given Vision's powers and his connection with the Mind Stone, that could've made him the strongest Avenger. Still, the debate wasn't settled yet.
Cut to Thor: Ragnarok, where it's revealed how Stark has nick-named Bruce Banner aka The Hulk as the 'Strongest Avenger' on the Avengers quinjet. That was probably because of Hulk's upper hand when it came to brutal strength and destructive capabilities he had against the team's enemies. In the meanwhile, with Benedict Cumberbatch's Doctor Strange pulling crazy moves like - bringing an entire army through portals and seeing right into the future, he was the strongest of them all. But now, with WandaVision's finale, the confusion over this debate has finally lifted. There are SPOILERS ahead.
The finale episode had Agatha confronting Wanda about her past and her role as Scarlet Witch; something Wanda has always been unaware of. Agatha also introduced Darkhold, the book of the damned, which was also speculated after Episode 7. Summoning Darkhold, Agatha revealed how Wanda is the most powerful Avenger as of now in the MCU. This is what Agatha says about Scarlet Witch.
"The Scarlet Witch is not born, she is forged. She has no coven, no need for incantation. Your power exceeds that of the Sorcerer Supreme. It's your destiny to destroy the world."
There you have it. Considering the powers Wanda has got and her abilities to perform several hexes to manipulate everything around her, she surpasses the Sorcerer Supreme in terms of strength and magical abilities. And this means, Wanda isn't just powerful as Doctor Strange, she was way more powerful than the Ancient One as well; thus making her powerful than any of her teammates among the Avengers. It's just that, Wanda has never been aware of her powers, and as she claims herself in the series finale, she doesn't understand them either.
And since she doesn't understand those powers; it's possible that Wanda would not be technically the most powerful for a little while more, not unless she's fully aware of her powers and their uses and abuses. The series revealed that Agatha's fears against the powers of a Scarlet Witch are real and Wanda could be potentially dangerous. The people in Westview are exponentially pissed at her for what she made them go through. Wanda may not be bad at heart, but what the unrealized strength of being Scarlet Witch would lead her to would spawn a whole different story for the viewers.
We know that it's the series is the first time Wanda is addressed as Scarlet Witch. For the MCU version of the character, the name Scarlet Witch is not just a nick-name but is her personal backstory and probably connected to the origins of her powers. The show has already hinted that it probably wasn't the Mind Stone that gave Wanda her powers. From what it seems, the powers of Scarlet Witch are possibly passed on and have been possessed by many over the years since the 17th-century Salem Witch Trials, or maybe, the powers have possibly killed the possessors until Wanda. It's quite a mystery for now how Wanda got her powers, but she was not always Scarlet Witch in the MCU. And now that she finally is, new lore surrounding her has just begun within the Marvel Cinematic Universe.