This applies to Luffy’s crew and the Supernovas too. None of them are new Luffy’s level. Not even Zoro and probably not Kid. Either there’s going to be a Timeskip, or they’re all going to be making some major leaps in strength. Most of his Crew doesn’t even have CoO and CoA yet. Also, Koby is almost certainly stronger than Pre-Skip Smoker. He’s mastered Rokushiki and he has Haki. His CoO is on an advanced level and he’s been sailing in the New World. My best guess, is that he’s weaker than Sanji and stronger than Franky.
I can see your point, actually.
But, here is my take on it.
First, even though I'm Sanji fan, I do not believe he'll be stronger than an admiral to begin with. I think Sanji will be in the range between YFM and an admiral. And if he won against an admiral at EoS, I think it will be through exploiting a weakness and through nullifying his abilities (which isn't necessarily a feat based on his strength be above admirals)
While Zoro will keep his edge over Sanji in strength by defeating an admiral through his sheer power.
Secondly, I am not a believer of Supernova to reach admiral level except for Kidd and Law.
And both are higher in level by portrayel from Zoro and Sanji (in my book). At least for now.
And then again, the SH crew SPECIALLY gets more growth in strength than other characters because they are main characters and they are main focus of story and every arc, we follow their growth.
So, despite that, and I still put Sanji in a level between YFM and admirals.
Luffy is the only person who will surpass admirals by clear margin, while Zoro will be barely above an avarage admiral. And Sanji just barely beneath them.
So, accounting all that, I respect your point of view, but I bepieve the best level Koby can achieve is be on Sanji level at that time.
But becoming an admiral, I do truly believe that it will be AFTER the war ends.
Also, people shouldn't take things literally. Logic should be applied. As an example, Koby told Luffy in water 7 that the next time they will meet, he will be muuuuch stronger and capture Luffy.
What happened? He got oneshotted in marineford.
So, we shouldn't take things always as it will happen. Sure, Koby will become what he promised, but it isn't necessary to happen before the final war ends.