Nika embodied everything necessary to be top 1. He had power, had will, had a sword, and a shield.
But was ultimately alone.
Luffy has someone else's fruit, someone else's will, Zoro as a sword, Sanji as a shield, and the rest of the SHs for whatever other needs he has.
Luffy will triumph because he doesn't do everything himself (on paper), instead trusting others to help him.
The "power of friendship" is what will make him PK.