I give this to Eternity and Infinity. Galactus would have to eat a whole universe to be on their combined level. In the Black Celestial Arc he was just in the process of doing that. Who's to say he could have coped with all of that power? On top of that Galactus was just a eating machine in that story arc, he wasnt aware of his surroundings he was in a trance like state and focused purely on eating. How can he fight like that? Who is to say he could?
Our Galactus eats and then he is satiated for a while until he has expended his power. If this BC arc Galactus is constantly hungry then thats because hes constantly burning off his energy reserves at a rapid rate thanks to the Dreaming Celestials alterarions. So who is to say that he would have the power to fight whilst in this state?
Further to that point, what feats of power did you see this Galactus achieve but eat? There werent any, because as far as we were shown he was locked into that state and was in no position to do anything else. He even required the F4's assistance to take his own life.
As far as we were shown he was just an eating machine. He was constantly hungry because he was altered to constantly burn off his energy. He'd have nothing to use in battle. He's not conscious enough to fight even if he wanted to. We have no energy manipulation feats, or feats of any kind to make him anything but outclassed in this match up.
Admittedly it was speculation, but that was obvious given how i referenced 616 Galactus' nature as the reasoning behind my view.
Regardless, my other points still stand. Who is to say that Galactus would be in a position to fight the likes of Eternity/Infinity combined?
He hadnt eaten a whole universe yet because he didnt have a chance to. He was locked in a trance like state only briefly coming out of it when attacked. Thats all the opportunity his opponents would need.
On top of that, what feats did you see this Galactus achieve with this power? None at all. Who is to say he was capable of wielding a level of power exponentially greater than he does as standard?
He might not have been able to control it. Again thats an opportunity for his opponents who by their nature can wield that level of power.
All we saw him do is eat. And that was down to alterations by the Dreaming Celestial. That is all he was altered to do because the Dreaming Celestial wanted to start his own reality in the void left behind. It wouldnt make sense to empower a potential foe with the power of a whole universe and the capability to use it.
This BC arc Galactus is an unknown so he cant effectively be used in forum match ups. He is just like the original Superman Prime.
iirc, the Black Celestial wished to use Galactus to eat away the entire universe and ultimately destroy the Celestials in the progress, then the Black Celestial who had been using some kind of machine to shield himself from Galactus, would afterwards (when Galactus was done (with the universe/multiverse/omniverse whatever)) become the Founder of a new Universe.
I don't think the Black Celestial counted on Galactus to defeat those you listed in a traditionel sense, but rather simply begin to absorb them along with their energy.