I'm only 10 months in, and the sensitivity seems to come and go sometimes for me personally. Though lately they have been super erogenous, more than usual, and it's so hard to keep my hands off some days lol. I am on progesterone and estrogen, so the progesterone may have an effect. I know a few trans women who's breasts aren't very sensitive. Like Cis women, sensitivity varies. I remember my first time, and even to this day, touching my breasts sometimes makes my legs buckle from under me. Something as simple as lightly brushing them can cause it. But some cis women may have sensitive breasts, others may not, it's kind of a luck of the draw and how your breasts grow and several other factors, but generally, it varies between people how erogenous your breasts are.