Again he has almost no feats.But I dug around and I have one:-
Moondragon connected to him and felt his emotion w/ relative ease.She says it was deafening which I guess got Jean.Although Jean managed to make sense of it's thoughts so there's that.
Either way 2 Telepaths have shown they can affect Knull, and Daredevil fought of his influence...
It's simple
"Nightmare is a Class Three Demon who is able to capture a sleeping person's astral form and bring it to his realm. There they are tormented in various ways as he chooses,he can also possess people to work through them."
He hadn't brought any of them back into his realm
"
Weaknesses
Nightmare is much weaker when outside of his realm, and can be overcome while in it by a being who has completely conquered their fear."
https://marvel.fandom.com/wiki/Night..._and_Abilities
It's all there.His only major weakness is that he's far weaker outside his own realm than when in it...
Yeah, and the Hulk has limitless power and has connections to TOAA/TOBA which is more than omega level.Even Spider-man himself has discovered and harnessed Beyond Omega level energies.
Neither of them are on the level of cosmic abstracts.
Omega is more of a "limits that we haven't found" than "limitless".If it wasn't then reality warpers alone would make Arrako, there would be no need for all the other omegas.
Jean in this current era can't go through Magneto's defenses when he's laid down
w/out his helmet or go through Psi-dampners.You can't have a character who can w/out any plot devices influence/access cosmic abstracts and yet can't pull these thing off.(I'm not saying she shouldn't be able to do these things btw, I'm saying most writers will have to do these because she's already working on levels below her.Same way Spider-man can't OHKO most of his Rogue's even though he clearly has the feats to)
Oh also for more Knull things:-
"Before anyone starts with the "huh, he goes from Big Bang to sun level, must be jobbing lel" Note that that Knull was nerfed unknowingly as the unique energy connection he had to the headless Celestial (the one he killed way back last year) which provided power to the All-Black, as well as him in general. Therefore, anything after the Cosmic Thor fight is Knull nerfed. (King in Black- Return of the Valkyries #4)"
Jean's TP feat happens in KIB 4 after the fight w/ Cosmic Thor(KIB 3), and he'd lost a lot of power as mentioned above.This just like Nightmare not being in his realm when facing of w/ Jean should be noted when power-scaling her feats.
Also Thor struck one of Knull's symbiotes with so much power that Knull got overpowered and lost his control over millions of symbiotes.This is what I'd call a massive feat against Knull's psyche
Storm herself was overwhelmed by Knull's forces and everyone knows she's one of the strongest omegas our their so there's that.Storm's lightning even hit Knull's dragon but Knull felt no pain other than saying "hemm, hello little light".
Further showing being omega doesn't mean one is limitless or even the strongest.Amongst mutants I'd agree but just like there are beings stronger than Hulk, there are people stronger than Omegas in their field
If you need more scans for some of these statements let me know