Anyone who actually thought this was a serious plot point that needed solving was delusional from the start lmfao. The entire OP world was in unison agreement that Luffy was a Yonko, the fact that people thought Luffy would need to prove himself to Lucci is just hilarious
If anything Luffy should prove to Kizaru that he is a Yonko so that Kizaru might finally start taking him seriously
But nah we need to send Laturn flying across the island just so Luffy and Sanji can gang up on casual Kizaru together