It's not the exact same scene though. 1. Zoro didn't use the same move or his own equivalent I.e. Hiryu: Kaen, instead he used a 3 style move against an attack that looked like a dragon...clearly not the same at all.
Also tbh zoro has done enough. First the rooftop, now king. Kaido is Luffy’s fight. Kaido knows shit about Joyboy, which is crucial to the story.
No he hasn't, is the job finished? I don't think so...Kaido is still breathing. So what? His whole goal throughout the arc was never to just scar Kaido, or defeat King. It was, as he has repeated multiple times, to kill Kaido. Luffy can still find out about "joy boy", even though I don't know why Kaido would just tell him that, beat Kaido in a fight and still need assistance if/when Kaido recovers (awakening), something Luffy does not have the ability to do.
Zoro intervening makes absolutely sense, just look at his goals and not the typical "but luffy MC so 1 v 1 main villain."