To be fair, if Kuma and Bonney can free themselves thanks to Luffy, and literally becoming/using Nika, is even better.
Luffy will always have the big slaver himself, the root of all the evil, Imu, so having his lackey too is not that mandatory.
In fact, that could do justice to Kuma and Bonney more while Luffy close the circle started in Sabaody (even though, I do not think it will be a conclusive fight).