A single throwaway line does not supersede on-panel feats. And like you said: CCUs and Cube Beings have feats that are infinitely superior to most of the Celestials. Granted some of the Celestials have very impressive high-end showings, but on average the race as a whole are dwarfed by Cubes.
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"I am tired of Earth. These people.
I am tired of being caught in the tangle of their lives."
Seeing as it was kubik himself who noted his inferiority to the celestials, you can't ignore it based on the fact that they have more feats.
Cube beings have feats above most abstracts. Even the multi versions ,I would love to see someone say they could beat a multi abstract too. Better yet why not say they could take on tribunal or Toaa too since their feats are more ?
We have a DIRECT comparison between them which you can't throw away because you don't like it. Kubik has no reason to lie or be afraid
Their universal and co feats don't mean a celestial can't replicate it. I don't remember a celestial failing to do so when it tried and I don't remember a celestial losing to a cubed being In a fight either
That was another reality
Alternate celestials have ranked alternate IGs and UNs
Alternate galactus was stronger than LT
Kong hyperion killed another alternate galactus
Etc