Saying Apoc could mount an offense against Galen is a terribly bias argument. It assumes Galactus has the perception and awareness of a child. It also implies that Apoc's powers are more fundamental and versatile than Galactus...as if Apoc could grant himself any physical power and size and all Galactus could do is blast him with Cyclops or Jubilee level attacks.
IMO Galactus' cosmic awareness would detect the threat from Nur. Seeing that Galactus' powers r so elevated i.e. he once showed the godly hercules that he could turn him into an amoeba and then back again, he would also have the same domain over Apoc...If he had domain over a being who was protected by the enchantments of Zeus then Apoc should be his plaything...probably turn him back into a low level mutant or even into a plain human...Or he could do him the same way he did Sphinx(who was more powerful than Nur) and send him into a loop in the timestream where he is beaten by Galactus over and over for eternity.
BTW Galactus' body is only a manifestation of his true form, trying to damage it physically is of no significance. He appears to an individual however he wishes to appear. Thus as long as his power level is sufficient he could appear the size of a planet like a Celestial or he could be small enough to engage with humanoids...one time the Thing carried Galactus' seemingly unconscious body in one of its smaller manifestations.