Luffy's goal wasn't to kill or stop Enel from leaving Skypiea but making him leave the island. If Enel just woke after that to terrorize Skypiea again and this time, someone else beat him, it wouldn't really be Luffy defeating him imo. He would just be a major player. If Luffy makes Kaido leave Wano then that's fine by me. Honestly, if Zoro kills Kaido while the latter is trying to escape Luffy, it'll still be Luffy defeating him. I don't know if it'll look good on Zoro though.