Sometimes you have to get a witch to finish the job. Scarlet Witch is one of the more powerful Marvel characters. She carries a wide range of powers such as mind control, healing factor, control of elements, chaos magic, and much more. In the films, she is as strong as almost any other character.
She can also do something that many of the other heroes can accomplish– destroying infinity stones. After figuring out how to crush those stones, she has what it takes to take down a gemless Thanos.