Always has been:
First Two Straw Hats (Zoro is actually only SH that Luffy wanted to add him before meeting him)
Zoro is only SH who defeated his own Arc Villain & not Luffy, clearly portraying them to be Similar
Oda created Two New Generation Marines to reflect this Duo & they are Koby & Helmeppo
Oda again created another Marine Duo to reflect on Luffy/Zoro & they are Smoker & Tashigi
This Trend continued with so many others including: Croco & Mr. 1, Lucci & Kaku, Roger & Rayleigh, Shanks & Beckman ... etc
During East Blue, they were put together so many times & many Characters were confused on who is Captain?
But this actually continued in almost every Arc, where Characters thought Zoro is the Real Captain!
After Alabasta Arc, Oda decided that only Luffy & Zoro shall have Bounties
And he decided that both Bounty Posters should have Usopp in the Background
During Baratie Arc, Sanji was inspired by both of them & they were treated as a Duo by both Mihawk & Zeff
Oda showed us that they both Met their End-Goal Character & cried & vowed to Surpass them one day
And Oda made these Two Characters Rivals, which is no coincidence
Oda decided that both Characters should have an Eye Scar since start of Story & both should have Chest Scar
Oda dedicated a Full Chapter for Luffy vs Zoro (Named it so) where they had a Draw & they themselves weren't sure who is Stronger
Both of them had Bounties higher than Bellamy & both of them met Blackbeard & had that Unique "They" comment
Both of them were part of Eleven Supernova & later on Worst Generation
Both of them are compared to Oden & must surpass him together
Oda dedicated a whole Volume of Water 7 Arc where Luffy & Zoro literally share the same Scenes over & over again
Both are fighting Yonko & faced other Supernova together
Monet said the exact same word to both of them claiming that she cannot hope to defeat them
They are only Two SHs who had their 2 Years solely focused on Fighting & had Top Tier Masters, other SHs had Guardians/Allies instead
They are only Two SHs who were Introduced differently than other SHs after Timeskip & both Introductions implied how Strong they are
Zoro is clearly gonna show CoC soon adding another thing that enforces this Duo
They both fought & grabbed interest of Fujitora who was a Side-Antagonist, which also happened with Mihawk, Kuma & Blackbeard
They are both highlighted as Leaders of New Era from Yamato's retelling of Oden's Prophecy
And much much more, making a Thread with Panels showcasing every single Detail about Luffy/Zoro Duo would destroy Zoro-Haters permanently
tf is this? 
