Well, there are certain aspects of the "formula" that are common place in this kind of story. You know Luffy is going to fight the "big bad" of each arc. You know Zoro is going to fight the sword guy. You know Nami is going to fight some chick usually.
That's the basic formula for the series. Would it be interesting to see things more mixed-up? Absolutely. I still think Sanji should have fought Califa instead of stepping aside for Nami, and Usopp should have fought Jyabura instead of stepping aside for Sanji.
But we usually know that Luffy will fight the head bad guy, Zoro will fight the #2, and Sanji will take on the #3. But now we have another swordsman - not every arc will have two sword guys in it, which means Brook joins Usopp and Chopper as the "comic relief"/"Scooby Doo and Shaggy" team of the Straw Hats that runs around doing stupid stuff and pouring salt on people. And you got Franky who can fight from a distance and also punch them too, which definitely detracts from Usopp's worth in fights as well.
To keep things on topic, the fact that there are now 2 swordsmen, and 2 guys who can shoot, coupled with similar Devil Fruit powers recently, could hint at Oda starting to slow down a bit creatively. He's been doing this for over 10 years, so I think it's only logical to reach a creative peak. It's still good, and things are very interesting at this point with the big picture stuff, but the details are starting to show some signs of aging.