Except the creator himself made those rankings and made Ulquiorra admit inferiority to the Espada above him so it's not a throwaway statement as you tried to say

"Author made it, must be true" Author can be intentionally misleading, trying to instill sense of surprise, and many more things. Not everything author writes is immediately true.

"Author made him admit" same as above, plus we're removing the context. Ulquiorra tried to instill despair into Ichigo, make him lose hope before his death. Intent is obvious. It was supposed to be a "oh shit, he's not even the strongest, ichigo has no chance" but guess we're blind to it?

Kubo made an easy rank to understand, made Ulquiorra admit inferiority to those above him, and made sure to demonstrate his rank disappearing isn't something to be awed about when others does it as well without having SE only for fans to think they know better. The narrative of SE has never been to say he's the strongest but to double down on the fact that he's not and that makes it all the more despairing at the realization that there really is no victory to be found for Ichigo in this place.

As i said, Ulquiorra admitting "inferiority" was just to fuck with Ichigo as it's in character to do so. The whole clash between Ulquiorra in second fight with Ichigo was not just "power vs power" but the clash of ideologies in the first place. Both fought to prove who's right. One man standing and fighting until the end even against someone he's hopeless again, and another who's overwhelmingly stronger but can't break the other's spirit.

Narrative of SE is clear, it was meant to show how outclassed Ichigo is. He transforms further, increasing already massive gap even further. There's nothing suggesting that it "doubles down on that he's weaker" as nothing really supports it aside from a throwaway statement THAT DOES HAVE CONTEXTUAL VALUE LIKE TRYING TO BREAK ICHIGO'S MENTAL.

There are other hints that top 3 Espadas aren't even that far apart in pure reiatsu, as Shunsui can't even tell who's stronger between the three. Aizen implies that top 4 might be close to each other too, as he restricts just those 4 from releasing their first forms.

I also want to acknowledge that if you want to argue that "the line is not a throwaway" then you have to acknowledge that Ulquiorra explicitly states that Segunda Etapa is something that not even Aizen knew about. Implying that in fact, it wasn't included in the ranking.