I should start this off by saying that the only type of Marvel content I have consumed is within the Marvel Cinematic Universe (MCU). I haven’t read the comics and I’m writing this from what I have noticed from observing material from the MCU.
In my opinion, Wanda is one of, if not the most powerful avenger. While she may not be as physically strong as other characters, she does hold a lot of power. I will admit that Doctor Strange, Vision, Captain America, Iron Man, and Thor are all very strong. However, I believe that Wanda holds more power than the others listed above.
First off, in WandaVision, Agatha Harkness says that the Scarlet Witch is more powerful than the Sorcerer Supreme. Since Wanda is the Scarlet Witch and Doctor Strange is the sorcerer supreme, Wanda already is more powerful according to the Darkhold. The Darkhold, for those who do not know, is an ancient book of spells and is seen as the “book of the damned”. I have also seen some argue that Vision is more powerful than Wanda, but Wanda got her powers from the Mind Stone and killed Vision, as well as destroyed the stone. So, that argument is kind of irrelevant in my mind.
Now, I will admit, Captain America and Iron Man are pretty impressive as well. Even so, Wanda put a hex on both characters in Avengers: Age of Ultron, and it throws them off their game. That was also when Wanda knew nothing about her powers so who knows what she could really do to them with her knowledge now.
Lastly, I understand that Thor is a god and can control lighting with his big powerful hammer. I also remember when Thor held open a giant metal device and got blasted by a giant star, but I still think Wanda is still more powerful than Thor. For starters, she can put a hex on him and throw him off his rhythm like we saw in Avengers: Age of Ultron. Also, I think that Thor isn’t as powerful as he is without his hammer, Mjolnir. In the beginning of Avengers: Infinity War, Thor can’t do anything to stop Thanos from gaining the Tesseract because he doesn’t have Mjolnir. Thor can throw a mean punch, but I think Wanda can definitely humble him with her chaos magic.
On top of that, Wanda has no need for incantation. We learn in WandaVision that it took Agatha years to gain the amount of knowledge she possesses. However, for Wanda it can take a matter of minutes for her to acquire a new skill, such as creating runes.
Also, when battling Thanos during Avengers: Endgame, she could hold her own while Captain America, Iron Man, and Thor could not. She also most likely would have defeated Thanos if he hadn’t called an airstrike on the battlefield. She also stopped a bomb from going off when she was younger just from a thought, touched an infinity stone, can create and manipulate reality, not only recreate Vision but also created her children, and can enter into the astral dimension (something not even Doctor Stranger is not capable of).
We’ve only seen Wanda use her powers with little knowledge of what she actually can do, and with every new addition to the MCU we see her understand her powers more and more. The Scarlet Witch is already the most powerful Avenger, and her power will only increase with time.