Every Character here supports the argument that Espada rankings are wacky
The fact that characters such as Wonderweiss and Luppi, who are not Espada, but are still High - Mid Espada level shows the misconception of these rankings being absolute.
Kubo established the Espada to be 1-10 and then that is contradicted in the Story itself via Yammy.
Ulquiorras Segunda Etapa is arguably not Ranked because Aizen arguably didn't know about it. However, if he did, which he probably did, Ulquiorras rank is still contradicted by his own words "There are Three Espada above me", and yet, there are seemingly Four + Wonderweiss who is Espada level. And given that Ulquiorra literally had a Second Release, and no other Espada did, it implies he at least transcended his rank bare minimum.
You can say "Well Ulquiorra didn't know about Yammy", but he was the closest to Yammy, and it is stated that Yammy admired Ulquiorra. In fact, he was the only guy he respected.
Furthermore, Grimmjow himself says it's bullshit. Now you can just say he's being the cocky brash guy he is, but given the previous context, and the fact Nel, despite being 3, was surpassed by Nnoitra. It evidently shows there are still massive inconsistencies.
"But Kubo did the rankings, he ranked every Espada" and yet Kubo also contradicts this and adds several outliers. And Bleach isn't exactly a story that just hands everything to you on a plate, there is Nuance to it. But for some reason nobody likes this argument.
In fact, Luppi actually has comparable feats to Harribel given what he did to Toshiro, and yet Harribel couldn't finish him off so quickly in her Released State. And Toshiro said he needed Bankai against Base Yammy, who is 7 tiers below Harribel.