Its not gonna be it.
But lets face it, there are many manga with girls look much much more similar one another.
With one piece theres perona with her eyes, robin with her nose (and eyes), nami with her cheerful look, hancock with a hair that doesnt change unlike robin, vivi too has same style of hair each passing time, i think etc. If you line them one by one, you could see the differences.
Just because other manga might have the same issue doesn't excuse that One Piece has this issue and it has become such a problem to the storyline when it should not ever register. I think I speak for a lot of people when I say that the reason people are annoyed with Oda's repetitive women is the fact that he can damn well draw women with different faces and physiques and he just doesn't. Take a look at Perona or Praline or heck, the gender-bent anythings that Oda draws. The women there look sooo diverse!! (I really wish he'd drawn Apoo as a woman, such a design). That's what annoys people (or me at least), he can but he won't and this was the last straw. People went wild on the theories because they couldn't tell from a glance who's who and took up (is still taking) so much discussion over such a thing.