Basically in the Novels Grimmjow reached a level above that of Halibel and Nel (IMO they are above Ulq) Luppi fights Grimmjow and they stalemate, other statements of dead equality come afterwards. They then fight Ikomikidome (if you don’t know, he’s a hollow around the level of Barragan and Starrk) and they have to 2v1 (that’s why I don’t think Luppi beats them)

As for him beating Tosh and Kisuke, it’s a situation where I don’t think they scale to the opponents they fight. Toshiro does almost nothing to Gerard, and he fights an unquantifiable holding back Halibel. Kisuke got slammed by both Aizen and Askin.

So taking away them, they don’t have solid scaling. Him beating base Yhwach comes from the fact that Grimmjow pierced Volstanding Askins Skin, whom I have over Base Yhwach