The superpowers of Wanda and her twin brother Pietro come from HYDRA's experiments with the Mind Stone, which was previously embedded in Loki's Scepter. The Infinity Stones are known to awaken superpowers in living beings. For instance, the Tesseract gave Captain Marvel super strength, flight, photon blasts, and her Binary Mode; the Mind Stone gave Vision a conscience, the Soul Stone made Red Skull immortal, and the Mind Stone helped Doctor Strange defeat Dormammu inside his own dimension. This is why Wanda's powers are so strong, but her genetic disposition  - which may be the beginning of the development of mutants - also accentuates her abilities. Besides, Wanda's anger has increased her power level, and WandaVision just revealed that she now could hold her own against a Celestial.

Related: Spider-Man: Far From Home Hinted Fury Knew About WandaVision's Westview

The best proof of Wanda's immense power came in  Vol. 2 to terraform Earth and other planets. If Wanda's goals were aimed toward conquest, she could easily use all of her power to swallow up huge landmasses — and possibly the entire Earth — all alone and without breaking a sweat.

Fortunately, Wanda's only goal is to have a peaceful life with Vision. But still, she claimed a small portion of the planet and, quite literally, made it her own. Wanda also transformed S.W.O.R.D. into a circus, which is a representation of what she thinks of the intrusive organization. Ego didn't have the freedom to choose how the planets he terraforms would look, and his method of expansion makes him more reminiscent of a galactic-level parasite rather than an intelligent entity. All of this serves to prove that it's better to keep Wanda from switching to an offensive stance because if she does, hardly anyone would be able to stop her.

As Wanda's power grows, she becomes more prone to losing her temper and lashing out, which would possibly require the intervention of Doctor Strange and the beginning of Vision's dying body and so effective that it demonstrated how Wanda could change reality to a greater degree if she wanted. Perhaps if she's pushed over the edge a couple of meaningful words can finally break the multiverse open and introduce mutants to the MCU.