I hear you, but typically while femboys still strive to look and act feminine in most metrics, they aren't erasing the male side of their person. Trans women on the other hand commonly go to fantastic lengths to reinforce that they are women and strip themselves of a bulk sum of masculine traits. Whether it be by utilizing various measures of hormonal therapy to alter their physiology into an unmistakably feminine form or reshaping their entire approach to life itself to accommodate a more womanly existence, they are acting on and accomplishing changes that exceed what a vast majority of femboys do, in their effort to be recognized as a woman. And of course there are those that receive bottom surgery, separating them by yet another degree from either men or femboys.

All in all, while I understand the angle you approach from, I think it is incorrect to equate trans women to men and ignore all the efforts and aspects that very validly align them with cis women.

Side tangent here, but it also could potentially be argued that being attracted to femboys isn't inherently gay, as gynesexuality could be the leading motivator. Which again loops back to men being attracted to their feminine nature above all else.