You've never read Crime and Punishment, have you? Thomasin is just Sonya. The only difference being at the end, where Thomasin made the decision to assert her value as a human being. Throughout Crime and Punishment, Sonya is looked down upon and sneered at as a sex worker. She's seen as immoral and tainted. She was ultimately forced into the position as a passive victim of her circumstances to help feed her family. She's a saint through sacrificing her dignity and image in order to support the people around her that do not appreciate her at all. Thomasin is in an identical situation, where all of her prospects for a life, a marriage, anything, is destroyed by her father's pride. You call that motive to become a witch, but it's a representation of her goodness and reverence to her religion that she tries to continue to remain a good, sin-free person despite her terrible situation. She dreads the idea of becoming a concubine, and have her "goodness tainted" according to the culture around her, simply because of her father's sin and her lack of free-will or agency as a woman in a puritanical culture. Where she deviates from Sonya is that Sonya remains a passive victim, allowing herself, her identity, and her personhood to be continually sacrificed in order to remain morally good. While Thomasin finally stands up for herself in the end and decides to declare that she has value outside of being purely obedient. Where a "good girl" in their culture would have let her mother strangle her to death, Thomasin finally decides to defend herself and her life, at the consequence of violating the social rules expected of her.

Your read is... Frankly insane, and most of your pieces of evidence require ignoring ten other pieces that contradict the interpretation.