The Scarlet Witch proved her case as the Marvel Cinematic Universe's most powerful magic user in Doctor Strange in the Multiverse of Madness. No one came close to her power, including the Sorcerer Supreme himself. But many other powerful magic users exist in the MCU, including some that could potentially catch up to her.
Magic increasingly factors into the MCU in movies and streaming series and likely plays a greater role in The Multiverse Saga going forward. The franchise's strongest magicians potentially play a major role against Kang The Conqueror, including Loki and his many variants, all very powerful in magic.
Loki
Loki's skill in magic derives from his mother, Frigga. His knowledge and skill in magic prove extensive in his many appearances in the MCU, but he mainly relies on illusion. Loki excels in masquerading as other people, as he did with his father Odin for years, ruling Asgard and tricking all its citizens.
Loki also generates illusions to can appear to alter reality, making it seem like Thor's hand had been cut off. He also renders himself invisible at times, though his magic proved useless within the Time Variance Authority's domain.
Sylvie
Sylvie, among the most powerful Loki variants in the MCU or the comics, possesses extraordinary skill in magic. She primarily specializes in enchantment, able to manipulate some people to do her bidding. Her power exceeds even the Time Variance Authority's suppressive efforts inside their realm, where the Infinity Stones are just paperweights.
Sylvie also generates green energy bolts and blasts derived from magic. She mostly uses these for defense, but she has used them to attack others, particularly Loki in their battle over He Who Remains.
Wong
Wong reigns as the current Sorcerer Supreme in the MCU and earned the title thanks to his incredible knowledge and wisdom. He wields knowledge of mystical texts and objects that appears to exceed Doctor Strange's. Wong knew the location of Wundagore Mountain, the source of the Darkhold, which only a few know.
Wong generates portals and magical shields with relative ease. He also casts complex spells, using them to help defeat Gargantos, the tentacle monster that rampaged through New York City in Doctor Strange in the Multiverse of Madness.
Clea
While Clea's powers barely got explored in the mid-credits scene for Doctor Strange in the Multiverse of Madness, she displayed real power. Clea tore open a portal to the Dark Dimension with a blade and demonstrated knowledge of incursions between universes, hinting at vast knowledge and skill in magic.
Comic book fans know Clea hails from the Dark Dimension and is the niece of Dormammu. She wields incredible power, so much so that she eventually becomes the Sorcerer Supreme herself.
Agatha Harkness
Agatha Harkness numbers among the most powerful magicians in Marvel Comics and the same is true in the MCU. She possessed the Darkhold for a time and used it to prolong her life by centuries, though her true age remains a mystery. She also siphoned magic and living energy from living people, destroying her own coven.
Her ambition and lack of morals make her even more dangerous, as she would do anything to understand the power that Wanda Maximoff displayed in creating The Hex in Westview.
The Ancient One
The Ancient One served as Sorcerer Supreme for many years, thanks to her effective immortality. She derived her long life and power from unrivaled knowledge in many forms of magic. This included Dark Dimension magic, which she used to defend Earth and also obtain knowledge of infinite realms and realities.
She resisted Dormammu's power and influence, demonstrating exceptional willpower. The Ancient One perceived time and space beyond most people and could manipulate time to some degree thanks to the Eye of Agamotto.
Hela
Hela demonstrated her astounding magical power immediately when she captured and destroyed Mjölnir. She rendered the enchanted hammer's power moot and then proceeded to destroy Asgard's defenses. Her greatest power in magic gave her the title of 'Goddess of Death.'
Hela resurrected the dead in Thor: Ragnarok, creating an undead army including the giant wolf Fenris. She also ruled Hel, a realm where disgraced Asgardian warriors dwelt after they died.
Dormammu
Dormammu numbers among the most powerful magical beings in the Marvel Universe. The ruler of the Dark Dimension possesses supreme power within his realm, controlling time, space, and reality on a scale that Thanos only approached with the Infinity Gauntlet. Dormammu exists in many ways as the dimension itself, with no real distinction between them.
Dormammu also possesses the ability to bestow his power on others, as he did with Kaecilius and may have done with Clea. He likely appears again in the MCU with Clea's arrival, which bodes ill for the Avengers. This nearly omnipotent entity killed Doctor Strange with little effort.
Doctor Strange
Strange escaped death thanks to the Time Stone hidden within the Eye of Agamotto and exploited the fact that the Dark Dimension exists beyond time. His knowledge and ingenuity, combined with his exceptional natural talent in magic, helped advance him to Sorcerer Supreme in short order.
Strange wields terrific skill in magic, which sometimes leads him astray. His personal ambition and adeptness at magic led his variants to acquire knowledge and power capable of destroying entire universes. He now possesses this knowledge and much more, reflected in the manifestation of his mystical third eye.
The Scarlet Witch
The Scarlet Witch rendered Doctor Strange and the entire magical contingent at Kamar-Taj powerless in minutes. Wanda Maximoff possesses singular knowledge and skill in chaos magic, born with an apparent natural affinity for it that played a still-mysterious role in her destiny as the Scarlet Witch.
The Scarlet Witch crossed universes, destroyed the most powerful superheroes with their combined might in Earth-838, and withstood the multiversal power of America Chavez. Only her own grief and guilt ultimately stopped her from taking America's life and tearing open the multiverse for her own desires.