Just Fyi in monsters the only person that saw Ryuma actually kill a Dragon was Flare (iirc Cyrano was already defeated by Ryuma prior to it). So the argument that the people in the capital have to see it doesn't really hold any water.
At this point, arguing ZKK will happen is just being stubborn and refusing to accept reality imo. There was really no reason for Oda to draw in King's flame dragon otherwise. Only sensible explanation for it is that he wanted to somewhat satisfy the desire for it.
Personally I feel this Ryuma parallel was already fulfilled on PH and was much better than this one but well I can somewhat understand why Oda decided to draw it again Wano given the Zoro/Ryuma parallels.
Zoro has already had is time in the sun in the Kaido with the scar he gave him, he isn't killing him.
Notion was always ridiculous imo and this chapter I think puts a nail in that coffin but well I digress