Curate, connect, and discover
This right here is actually why I love zolu so much. Zoro is devoted to his crew and his captain, but he isn't at all a Luffy worshipper. He knows Luffy's strengths but he's also well aware of Luffy's weaknesses and shortcomings.
Although he is similar to Luffy on a lot of ways, (I do love me a good dumb and dumber duo) he also acts as Luffy's direct counter in many situations, balancing out his personality. Telling him to step up when necessary, bringing him back down to reality when he gets carried away, and overall pushing him to be a better captain.
And the best thing imo is that he's not afraid to be harsh about it.
I am alway confused when people (generally ZoLu shippers but not only, nothing against the ship itself though) characterize Zoro and Luffy's relationship as "Zoro is so obsessed with Luffy that he would follow his orders like a living weapon, no question asked".
Because don't forget that Zoro's role in the story has sometimes been "non ironically yell at Luffy because he is doing something Zoro really has a problem with".
Like, how could you forget "If Usopp does not apologize and you welcome him back anyways, then i am getting the fuck out of here. We're pirates, not school children" ? I also remember a few "Hey Luffy you better take things seriously right now stop joking around" post time skip. Zoro is totally devoted to the Strawhat pirates and their captain, and was notably ready to risk his own death against Kuma to save him (even if at first he was like "if you stop me from becoming the strongest swordman you will pay for it") but he also has his own principles which are not always aligned with Luffy