While some people (one person in particular) are quite critical of the way characters in One Piece produce attacks as if from nowhere, I actually really like it. In comparison, in Naruto we see in great detail the conception and training for virtually every technique. Naruto has a strong focus on the character's growth as an individual though, it's about Him, about his learning, his personal journey. One Piece, on the other hand, is more about the overall journey, and what happens along the way. We kind of just trust that, yes, these people are training themselves on their own time, and we don't need it spelled out every step of the way. Whenever we see them on their ship they're always improving themselves in this or that capacity, Zoro lifting 400 ton weights, Usopp and Franky inventing things, etc. The timeskip of course is the biggest opportunity for this yet, where we see that they're all clearly improving themselves, but we aren't spoiled on exactly what they've done.
And so in something like Naruto the fights are all "wait for him to use that technique we know about." Whereas in One Piece, you never know exactly how a fight is gonna go. It's a very different focus on how the battles play out, it's not that they're "ass-pulling" techniques, it's that we're put in the same place as their enemies. We don't know what they can do, and really any fighter worth a damn isn't going to just let you know everything they can do until they do it. It makes them all feel more adult, more confident, more secure in their ability to fight.