when Zoro becomes WSS that will be his peak. After that he will defend his title or look to challenge other strong swordsmen; it doesn't mean any other swordsman will ever reach Zoro's level. Plus, like I said before, it's Luffy's shonen dude
Saying it's " Luffy shonen " tells me you would be ok with "Ichigos shonen" ,"Natsus shonem" ,etc too...