As I mentioned before, Luffy has hit both attractive and non-attractive women. Franky didn't have a problem attacking Baby 5 at Punk Hazard.
I don't think Oda is stuck in that mindset, however it's just not a common occurrence in One Piece.
Can you name some of these battle shonen series that trying to break the mold?
Japan isn't a very progressive country when it comes to gender equality, especially in the manga and anime communities. I like to assume it's getting better, but one can never be too sure.
It's harder to find in Battle Shounen but there are a couple of "good" examples currently running. World Trigger is a good one that's currently running in Jump. One Punch Man has had a couple of female antagonist, including in the current chapter. Assassination Classroom is a mixed bag with some useful female characters and some that are complete stereotypes. Hero Academy is still new but it's doing pretty well with female protagonists. Outside of Jump there's Magi and UQ Holder off the top of my head. Although these series ended, Medaka Box, Psyren, Beelzebub (original series), Soul Eater, and Kekkaishi had strong female protagonists too (Medaka Box's main character being female).
- I've barely read Fairy Tail, so I can't give much to comment on. But from what I've seen, it seems to treat its female cast similar to shows like Ikki Tousen, where the fighting females are constantly sexualized.
This is one among many of Fairy Tail's problems. Unfortunately it's not something exclusive to Fairy Tail (Bleach and Naruto do/did this a lot too), and these days in One Piece characters like Nami are getting more and more sexualized as time passes. But as you said, these series are written for boys as the main demographic.
I'm gonna have to call bullshit on this. I haven't read Bleach in years, so I hardly know what's going on there.
Naruto has some of the worst female characters I've seen in a long time. It's a known fact that Kishimoto has trouble with characters of the opposite sex, since he's mentioned it before.
There's not much to argue with Bleach. It's actually one of the few areas the series does a better job than One Piece in, although there have been a lot more female antagonists fights than protagonists (Rukia being the most recent months ago, vs the current arc with a handful of female antagonists). Of course one of Bleach's problems is throwing way too many characters at readers and expecting us to care about them.
I actually quit reading Naruto for a couple of years after the Pain saga and just caught up after the series ended (I don't regret my decision either). But I agree that Naruto didn't do a good job with most of it's female characters in terms of characterization, personality, and depth (Sakura has to rank pretty highly on the worst Shounen female protagonists list). But strictly looking at female Shounen fights, Naruto has had more of them (one of my favorites being Konan vs Tobi). Even the final fight prior to Naruto and Sasuke involved the Rabbit Goddess vs Naruto, Sasuke, Kakashi and Sakura (yes she was horrible here too, just noting it).
Instead of looking solely at the fighting spectrum, look at female characters who are independent in their own.
Bellemere, Kureha, Vivi (yes, Vivi), Kokoro, Otohime, Olvia, Nojiko, Dadan, Kuina....
Each of these characters have shown strong resolve and determination when faced with tough circumstances on an emotional and mental level. In a shonen manga, to have that many female characters play a role, in life and in death, is a testament to Oda's writing. There's not a lot, but he makes them leave an impression on the reader and the main crew when their story is told.
I do feel like there haven't been any One Piece women who have left that kind of impression in a while, but it's going to happen sooner or later.
I hope Oda does prove me wrong eventually. When I was a regular in the big manga thread I spent a lot of time complaining about Robin and other female characters not getting fights before just coming to terms with a lot of what you're saying (Japan's culture, Shounen series in general, etc...). I still would love to see Oda give her and other female characters more chances to shine in fights, but complaining about it week after week wasn't productive, so I decided to move on and focus on the other more positive aspects of the series. Even if it doesn't happen, One Piece is still easily one of my favorite Shounen series not including Full Metal Alchemist and Hunter x Hunter, and Robin is still a great character.