Make him more plot relevant.
Here's the thing, I like Zoro. He's arguably my favorite strawhat. He's had some of my favorite moments in the entire series.
He's also, at this moment, the most redundant member of the strawhats.
When I look at the entire crew, everyone provides a role that no one else can replicate, in terms of battle and the ability to help the crew acquire One Piece.
Luffy's the captain. He's the strongest and most charismatic. He can make allies with almost anybody.
Nami is the navigator. The crew would never get One Piece without her.
Robin can read the poneglyphs. One Piece cannot be found without her.
Franky is the shipwright.
Chopper is the doctor.
Usopp is the sniper and has been the jack of all trades mechanic/engineer of the crew. He's even beatan an opponent that even Luffy couldn't.
Sanji is the cook and can carry out great espionage tactics.
Jinbei is a great helmsman who saved the Sunny from being destroyed in WCI. He's also super strong with valuable experience.
Brook is fairly redundant in terms of swordsmanship, but he can also attack souls and was able to capture a Road Poneglyph from Big Mom, something no other crew member would have been able to do.
When I think of Zoro, I envision a character who is convincingly the first mate and beats certain opponents that no other character, even Luffy, can beat solely through his expert swordsmanship. When I see his portrayal, I see a Luffy who is less charismatic and not as strong.
His strength isn't totally clear because Oda at times wants to put him on the same level as Luffy but he also wants to play up the rivalry with Sanji, a character who has been shown more clearly to be inferior in strength to Luffy. As a result he'll sometimes fight a Luffy opponent but there will likely be some caveat for not being able to beat that opponent (either too injured or literally not being able to hit them). He'll also fight the strongest subordinate, but because Oda likes to play up the Sanji rivalry, that subordinate will usually have an ally who is incredibly close in strength and while Zoro will have tougher fights with his opponent Sanji will have a bit of an easier time.
Essentially, there has only been one time in the series that Zoro has beaten someone that you can reasonably argue no one else on the crew could have beaten, maybe even Luffy, and that is Daz Bones in Alasbasta. Since then his feats could likely have been replicated.
His role as vice-captain/first mate hasn't really been properly established either. Outside of his ability to cause mayhem with Luffy his role as a right hand has been sorely lacking. The more the story goes on and the stronger and more experienced future crewmates get the less he seems to take charge. There's barely been any instances where he straight up takes charge and leads the crew. Hell, Sanji had more of a convincing role of that when he lead half the crew against Big Mom's forces in Dressrosa. You could even argue that Jinbei has shown better vice captain portrayals when he practically saved Luffy from the brink of despair after Marineford, and when he took the initiative to make an alliance with Bege and convinced Luffy to take part in it in WCI.
The last significant first mate like role for Zoro was probably Thriller Bark's "nothing happened"...but once again Sanji was there to show he was willing to replicate the same feat. Now he may have likely died from trying to do what Zoro did, but the end result, for me at least, was to leave in that nugget of possibility.
So for me the following would go a long way to make Zoro a better character:
1) Actually make swordsmanship have meaning. Swords right now are just a neat tool, they're not exactly a necessity to be a top tier. We currently have no reason to care about black swords other than "looks cool". We have no reason to care about Mihawk being WSS because no one else in the world except Zoro seems to give a shit about acquiring that title.
So for swordsmanship to have meaning I would like to see an opponent that only Zoro can beat and only through swordsmanship. Basically, a super version of Daz Bones. I was hoping King would be that but that was less swordsmanship and more "Advanced COC GOES BRRRR"
Another possibility is to make a twist where Mihawk is working with Im and is a legit end game antagonist.
I would also like it if Laugh Tale has some sort of obstacle that can only be cut by an elite swordsman. At the very least it would make having a swordsman important in aquiring One Piece
2) Establish Zoro has the de facto first mate/vice captain. I don't mean put him on a color spread with other VC's, or telling someone like Franky to cover him in a fight.
I'm talking if something happens to Luffy that causes the entire crew to legit freak out. In that moment everyone, even Sanji, looks toward Zoro to see what to do next and he would be the rock to calm everyone and fight on until Luffy bounces back.
I want moments like this to happen but I'm not sure if they will since it seems like Oda doesn't like to make it where Luffy is outshined, especially in battle and Zoro beating an opponent that Luffy couldn't is likely to do just that. Plus Oda seems hesitant in making Zoro the clear first mate/vc/#1 whatever. It's not something I expect until literally the last chapters of the series.
TLDR:
Make him more plot relevant by making his swordsmanship more important and genuinely build him up to be the VC/First Mate.