ZKK:
-Concludes Oden, Ushimaru, Yasuie, Hiyori, Toko, Ryuma and samurai as a whole's desire and necessity to keep Wano and it's people safe, "take Kaido's head", avenge others who were killed/starved for the past 20 years. Zoro has ties to all of these people, Luffy doesn't, nor does he share their values. Zoro represents the samurai and their culture, while Luffy plays at it by dressing up as them.
-Proves that Kaido is, in fact, different from the smaller-time villains we've faced so far and can't simply be imprisoned or sent away, he has to die. This would help push the idea that as the story reaches its end, stakes have to increase as a result.
-Maintains the seriousness of the situation the saga has presented us with, from Doffy's operations in Punk Hazard/Dressrosa to those from Ebisu town who could only laugh as Yasu died. Go back to chapter 942 and look at Zoro. Tell me the last time we saw him this angry. Then compare that to Luffy in 1045 and tell me who still has a chance at keeping this arc from ending as a joke.
-Actually allows Wano to contribute to their own success other than stalling people and wasting time until Luffy can get to Kaido. When was the last time we saw one of the scabbards do anything? Seems like Oda's checked enough boxes that he can finally forget they exist and get to what he (and apparently you) actually wants - wanking Luffy and not caring about the logical failings you create, so long as you get a flashy powerup to boost sales. Your vanity regarding this shows you don't look beneath the surface, and so you brush ZKK off as 'wanking' when it's a lot more than that.
ZKK isn't about wanking Zoro, it's about variety in the areas of importance our characters have. Luffy can do some things that others can't, he can't be PK by himself - developments like 1044/45 challenge this. Luffy couldn't handle big mom while sanji could, he couldn't escape wci while jimbe/franky/nami give the crew abilities to do so, etc. Zoro is the only sh without any ability to uniquely contribute, until Wano where we're given the perfect opportunity. You should have a more open mind.