It wasn't a parallel it was a strength comparison. Luffy or Joyboy, awakened Nika DF, was compared to Ryuma to become he saved Wano by defeating Kaido. If you would have never defeated Kadio they would not have made that comparison.
Ryuma > current Luffy.
It doesn't matter how much headcannon people push or upset they become Luffy did not defeat Kaido in a 100% solo battle. Kaido fought multiple opponents, beat Luffy three times who was saved and protected during his battle against Kaido, and was carrying a island. If Luffy would have fought Kaido in a complete solo battle we would have lost.
Ryuma > current Luffy.
It doesn't matter how much headcannon people push or upset they become Luffy did not defeat Kaido in a 100% solo battle. Kaido fought multiple opponents, beat Luffy three times who was saved and protected during his battle against Kaido, and was carrying a island. If Luffy would have fought Kaido in a complete solo battle we would have lost.