I don't want to defend the Rebecca thing because I didn't like it either. It sucked that she didn't get a big moment and it was kind of sexist. Oda's maybe improved on that front in the almost decade since.
But Rebecca's entire fighting style was based around dodging and not hitting her opponents. She was fighting ONLY because she had to, not because she wanted to. And we got more from her flashbacks later on about the peaceful life she wanted back. She wasn't supposed to be a fighter, that's just what the situation was forcing on her.
The message Oda was going for, and I don't agree with it at all or like it, but what was being attempted was "if she gets bloody and hurts someone or herself, that's just another part of her life Doflamingo has ruined." And keeping her pure was a moral victory over Dofla's taint.
Again, I don't like that message at all, but Oda very clearly had a specific vision there of "someone that is supposed to be innocent should hold that innocence while they can." It wasn't taking away her dreams or denying her happiness… it was just avoiding getting the pretty girl into a bloody fight which is something Oda was really really bad about. (Look at how many times Usopp got a female opponent that he defeated by scaring them and never actually touching them himself.) But has improved on.
We also of course have Sanji and his refusal to ever hit a woman always being treated as a super positive trait no matter how much it screws things up.
But my main point is, Rebecca not getting a fight sucked, the same way Nami and Robin never getting fights sucked... but that in no one impeded her actual dream or goal in the end, she still got exactly what she wanted. Oda didn't subvert that.
And Vivi famously got punched by Luffy for not being a realist about people sometimes dying, and then helplessly stood there and yelled and cried until the armies stopped fighting under no actual action of her own. Her role in things wasn't to be the muscle either, even though she'd shown at least a little competence.
Oda having his dainty pure pricesses is a thing I don't like, but its there. He IS getting better about it, in the last two arcs especially since he's started loading in a lot more female fighters among Big Mom and Kaidou.