First thing first. Do we have female themas in One Piece at all. Lets put it to a simple test. Just 3 questions:
1. Do we have more than one female in the series? Yeah, we actually have quite a few, although they are minority in comparison to number of male characters
2. Do they interact with one another? Another affirmative answer, although at the beginning Nami seemed to be isolated from other females, but than we find out she had a sister, then they all meet Vivi, Robin joined the Crew, they met Lola and Camie, not to mention Kokoro, her granddaughter, Conis, Aisa, dr Kureha and minor characters such a Teracotta.
3. Do they talk about something other than men? Although two main female leads often discus behavior of the male part of there crew, they also talk about all kind of stuff like political history. This held also in discussion with females outside there crew.
One Piece passed the test.
Secondly how the females characters are portrayed. The answer they are all different. They vary greatly according to they life experience and natural predisposition. We have independent ones (majority) but also a few that are dependable, like Shirahosh, greatly Perona. We have female of different social status princesses (Vivi), criminal (Nami) and average girls, like Conis, oh and also crime fighters, like Tashigi. There are some women on positions of power (Tsuru, Boa Hancock, Big Mum) We have old women with different temperaments - Kureha, Kokoro, Nyon, but that also holds truth to little girls such as Aisa, Chimney and Rica, mothers or adoptive mothers acts in different way towards they children. Some are nasty, some are sweet an caring (Makino), some are smart some are dumb. They usually require some help, but this is fine as they also tend to take action, not just watch as men fight for them (not to mention men also sometimes need help). Oh and taking action is not only actively fighting (see Otohime, Conis). They are also not shown as perfect, as they have quirks and character flaws. Some of them are important to the plot and the team, others make just background, but the background that gives as feel of authenticity, the feel of ling world, not the world that just revolves around main characters. They are never reduce to one or two stereotypical gender roles. That variety is simply beautiful. I must say I'm very happy with female characters design in One Piece, though I must admit, I think males are even better.
As to visual designs. Here we have a little problem with unnatural hourglass body shapes and big breast every attractive female seem to have. I don't particularly like it, but it doesn't bother me much at the same time. See as bodies in One Piece are generally not very realistic, we have lotsa guys over 2,5 m tall, and guys shaped like lets say… Tamagon. On the other hand we have individual facial features, hairstyles, sizes and bunch of ugly or obese or old or plainly strange female characters, who still have interesting personalities.
I think they dress decent enough.