Luffys battles with doffy and cracker were not extreme diff, sure he took a while to beat them but he never had trouble beating them down in the real sense. Just trickyness. He did have help yes. When i said his first solo fight was kata i meant that. Sure brulee allowed him to escape but he did come back to finish the fight.
Zoro will have to get extreme dif fights to grow stronger. Rayleigh said as much for haki
As soon as zoro found a way to bypass it he one shot him. The same deal with his other enemies, they were all weaker than him overall. No reason to believe that king. A yonkos first mate would be weaker than zoro, if anything it should be the reverse by a good marging. I see no reason why oda would make it so and it would be ridiculous honestly. So yes i do believe king will be zoros first extreme diff fight
The reason zoro had high diff at most fights is because he only ever fought people who were weaker than him physically. Notice how he never fought anyone with hax or physically stronger than him. The reason luffy had extreme diff fights is because he keeps fighting people above or equal to his paygrade with hax on top of it. Mr1 was physically weaker than zoro and less skilled and overly relied of his df.