100% NTA.

I have a similar situation in my parenting/sibling structure. Mom resented me for being born too soon after my sister, which means I deprived my sister of her mother’s attention. And for me not being a boy, of course. So she always coddled my sister and treated me with contempt. I grew up to be independent and have a really successful career. My sister is totally dependent on her much older boyfriend and can’t do anything for herself. Sometimes when parents choose a favorite they are actually doing more harm to the favorite. A parent who will make it obvious who they prefer is a shitty parent to begin with, so imagine having that parent overly involved with your life. Neglect and abuse sucks, but I’d rather be in my shoes than my sister’s.