Originally posted by Bentley
Tiamut used Galactus because Galan is intrinsically more powerful, even if he may not use that power in his regular self he is potentially more dangerous.I admit that it's entirely possible that Tiamut beats a non-weaponized Galactus, luckily for us, this time the Celestials are facing exactly that.
No Tiamut used Galactus because Galactus just happened to be on Earth at the time and within the IMPRISONED Tiamut's power range. The IMPRISONED Tiamut altered Galactus to his very core and Galactus couldn't stop him. Think about that for a sec.