I think Oda took a gamble with it, it is his story after all, he laid some connection before Zoro, Shimotsuki and Ryuma. However, Oda also made sure that he would not undermine Zoro's character and achievements by not giving him a straight up busted male father and grandfather etc. Zoro's grandparents and parents are not some strong swordsmen (something like Oden, Ryuma, Garp, Dragon), of course this might change later on (I don't expect to or at least I hope not).
While still having a connection to Wano and Ryuma, Zoro is still every inch his very own self made man through sheer hard work. And this is what many people really want, just a random kid who dreamed a big dream and achieved it through his own hard work.