There's no reason for Luffy to lose on his way to the top, but he has. Zoro can too. Anything else is just bias bullshit in Zoro's favor.
Let me ask something.
What is the purpose of Zoro losing here?
The last time Zoro lost, he learned a very important lesson about his place in the world and it informed 1000 chapters of story so far.
So what exactly is the purpose of Zoro losing here again? So that he learns that he should've listened to Tashigi and become a sword hunter since he can never be WSS if he doesn't find good swords? Is that it? Because that's what the OP wants.
If you have another reason on the caliber of the mihawk loss as to why Oda should write Zoro losing here, then please present it. Because you know there's no way Oda is just going to write that to satisfy you specifically.
And btw, there is a NARRATIVE reason why Luffy loses and Zoro doesn't. You can just look at Alabasta. Both Luffy and Zoro are up against opponents who they literally cannot even harm. But do you notice the difference in intention of the fight?
Luffy must appear as an underdog hence why he can even suffer multiple losses. Zoro on the other hand meets Daz Bones and literally tells him he's so above Daz's level that he could only join Baroque works if he's the leader. And then Zoro beats him in their first encounter.
Even though both Luffy and Zoro face the same type of situation, Zoro wins immediately while Luffy loses a number of times. Kind of like the story has a purpose for why it's structured like this. Like there's a message somewhere here.