Claiming that zoro gets most development where he got NADA during swordsman arc with almost 200 chapters and his family tree on SBS is crazy.
This isnt naruto or hunterxhunter, there is no deuteragonist in OP.
Zoro's development revolves around a few hype moments for ZKK fans, but stops at that.
IF, and thats a big if, his family becomes relevant in the endgame, he could fight for being no 2 most relevant inside the crew, claiming his 2 most relevant in the show is literal mental illness.
Outside of that, you also have robin(current number 2 most important SH) with ohara, Saul and poneglyphs plot.
Nami who could very well be a celestial dragon or even more.
Chopper who's gonna find the definitive medicine to cure the laftel DF users disease...
Zoro is definitely a far second from luffy inside SHs crew strength hierarchy, but when it comes to plot relevance, he's far from top.