I know where you are coming from trust me.
But the issue i have is that even as a zoro fan, i am not comfortable putting zoro at admiral level just based on rooftop feats. But mid-diff King I can beyond a shadow of doubt put him at least admiral level.
I see it this way: if you want to solidify yourself as a top tier, you do it by gaining feats against other top tiers, not high tiers.
To be fair, I think what Zoro lacks to be firmly Admiral level are his presumed inexperience against top tiers in real life & death situation (which will force his haki to bloom extensively) and some of his stats other than his AP (which dwarf many top tiers) & durability.
Another reason: In general, top tiers in One Piece tend to grow alongside other top tiers (Rocks, Shanks vs Mihawk rivalry, and the Admirals, for example) to reach the level they are on right now. Zoro, unfortunately, does not have this luxury.
The SHs are not hostile like Rocks while the only fellow future top tier in the crew, aside from Zoro himself, is the guy he is trying to help become the Pirate King. This means constant internal threat like in Rocks did not exist for Zoro.
As far as we know, Zoro is the only swordsman that Mihawk encouraged to try to surpass him, so Zoro has no rival like Mihawk had in Shanks (which no doubt helped both grew).
And Zoro only had a constant training from a top tier in Mihawk after his journey was half-way, whereas the current admirals had constant direction from another admiral when they first became part of the Marines.
It is these factors that hinder him to 'officially' join the Admiral level, I should think.
However, his Roof Piece performance remains the best performance against top tiers since Akainu, despite the fact that he did not have the two elements which undoubtedly bolstered Akainu's performance in MF (an op DF and a top tier's failing health).