The Celestials are one of Jack Kirby's greatest gifts to Marvel.
I bet he was inspired by the ideas he saw in 2001: A Space Odyssey - he adapted that to comic form. The idea of the unseen otherworlders, shaping man's destiny from afar, acting as invisible benefactors. Even the idea of the Black Monolith - Celestials look as impassive as that object did, which would appear and vanish when it choosed.
And the Neil Gaiman/John Romita Jr. Eternals series looks great. I knew Gaiman could be counted on for smart quality of story with quiet poetry of ideas.
"I'm not smart so much as I am not dumb." - Harlan Ellison
The enormous Celestial Exitar clearly depicted above easily dwarfs Arishem, who is roughly 2,000 ft. If you compare the two, Exitar is equivalent in height as 5 or 6 Arishem's, making him around 10,000 feet tall atleast!