Ciswomen receive drastically lesser sentences for committing the same crimes as men. There's quite a bit of statistical information on this. This is just one of many, many examples of female privilege. If you're looking for more, you might want to read some of Warren Farrell's books, or Norah Vincent's book Self-Made Man. The fact that cismen have privilege and power over ciswomen in certain ways does not preclude the possibility of ciswomen having power and privilege over cismen in other ways. The analysis of gendered power that feminism has given us is, unfortunately, overly simplistic. Furthermore, the relationship dynamic and power dynamic between ciswomen and cismen is not the same as the relationship and power dynamic between the rich and the poor, or white people and black people, and this is partially because heterosexuality, which is characterized by an attraction of difference, is not only the norm, but is institutionalized in many respects. This is not the case for race and social class. Feminists were wrong to say that women are oppressed by men in the same way that the poor are oppressed by the rich, and the way black people are oppressed by white people. (Keep in mind that feminism has very rarely addressed the trans community and when they speak of women's oppression they are referring to ciswomen, not transwomen. When feminism has addressed us, they have treated us with indifference at best, hatred and malice at worst, or have used and exploited us for the benefit of ciswomen and ciswomen feminists. There are very few feminist scholars who have supported us or respected us in any way shape or form.) I could literally write a book on the differences between the relationship and power dynamic of ciswomen and cismen, and the relationship and power dynamic of every other more privileged majority group and their corresponding disadvantaged and/or oppressed minority group.
Also, I think what you're not taking into consideration is that there are two sides to a trans person's social interaction. One, how we see ourselves; and two, how others see us. I am a transwoman and have been my entire life. However, socially, throughout most of my life, people have seen me and interacted with me as if I were a man. As I transition, from my perspective, I go from being a transwoman who looked like a man, to, hopefully, a transwoman who looks like a ciswoman. (Although, even this is problematic as there are butch ciswomen who look like men.) This means that, from an outside perspective, it may seem as though I'm transitioning from a man to a woman. However, this is an oversimplification. If I ever get to the point where I'm perceived to be a ciswoman, socially, then I will gain the privilege and power that ciswomen have that many transwomen do not have. (Although, even then this power will be tenuous and only to the extent that I'm not found out to be trans.) The underlying issue here is one of social intelligibility, and it is one that is often overlooked.
