Guys like luffy has slowly progressed by taking on high tiers like doflamingo, cracker, katakuri and slowly became stronger, increased his stamina and endurance, had days long battle with cracker and katakuri, and increase haki levels and unlocked advanced versions of coa and coo.
Zoro didn't progress since post ts because he only had joke battles like monet, pica, hyozo. his only extreme battle was with kamazo, that if kid himself is high tier then kamazo is not more then mid tier.
zoro jumping from mid tier to beat top top tier makes no sense. he would have slowly progresses like luffy by taking on 3 high tiers since dressrosa, like luffy.
even jimbe had more training then zoro with his days long battle with high tier ace, fighting admirals in the war, fighting bm pirates.
