First of all, just because my opinion doesnt match yours, its not "ridiculious headcanon". If you want to discuss with me, dont do it that childish.
You base your opinion on the idea Wano is "Zoros main arc" and cause he said something he nearly says always. Thats your opinion, fine, i disagree, but thats it.
We dont know it yet, true. But at the same point, we cant assume he is Yonko level, out of nowhere. For sure he will have clashed with Mihawk in his training, but thats not the kind of fights Rayleigh was talking about. Rayleigh talked about fights against stronger enemies intending to kill you. Mihawk dont wanted to kill Zoro, he never wanted to. For sure Zoro will have grown up alot and i guess Yonkos First Mate is a huuuuge step for that and already extremely impressive. He dont need to be God Level out of nowhere and i dont get why this is such needed by the Zoro fandom?