The theory that Galactus is equal to Eternity is true...they are equals, (sort of siblings), but only in terms of importance...not power. It has never been proven that his Power Cosmic is on a level with that of Eternity. If I'm wrong, then feel free to show evidence.
Galactus can destroy a planet...well that's impressive...Celestials can do the same, and with relative ease, (ie. Infinity Gauntlet, where they were hurling planets at Thanos...logic would dictate that they could easily toss two planets at each other, destroying them).
Earth X...my favourite...everyone conveniently ignores that 'Galactus' was actually Franklin Richards.
Character statements: Watcher said Galactus was the most powerful being in the universe...Watcher has also stated that the Phoenix was second to God...and recently confirmed Squirrel Girl's victory over the 'true' Thanos. In conclusion, how reliable is the Watcher? His word isn't worth a damn, anymore.
If you really want to put stock into character statements, then what about Galactus' apparent shock when Thanos ripped a Celestial apart in 'The End'? Someone mentioned that Eternity regarded Galactus as a peer...well he's also said the same to the Living Tribunal. Does that automatically put all three on an even power level?
Someone else said that Galactus could even take down Exitar...a freakin' 20,000-foot Celestial...by and far the most powerful of the bunch. To Exitar, Galactus, (at 30-feet), would appear smaller than a mosquito would to the average human. I'm sure he can bite him...but that's about it.