Eternal Idol
Lono, "The Dog"
You're well-spoken, but clearly your reading comprehension is lacking, so I'll break it down for you:
The first Celestial not only acknowledges Galactus' cosmic role, but also his power and capability. The second Celestial acknowledges Galactus' interference could sabotage their plans. Galactus' presence, unexpected or not, wouldn't "skew probabilities" if he was no threat to them.
The first Celestial Galactus warns Galactus to leave or die, and lies about their intent in 616 to encourage Galactus to leave. Galactus dismisses the threat, reveals he knows their true intent in 616, and makes it clear he will fight them if they proceed.
The third Celestial goes apeshit and orders the others to kill Galactus, once again, confirming he is a threat to their plans. He prepares an attack, and is immediately blasted by Galactus, while he crushes the life out of the first Celestial.
Galactus halts his attack as the Celestials look upon their dead comrade. The only thing that makes sense to bring Galactus pause is that it was made clear he was their superior and they should heed his warning to return to their universe.
The Celestials had no choice but to merge with each other and their dead ally to defeat Galactus, an ability which surprised even him, likely because 616 Celestials have never before demonstrated the ability to merge and combine powers.
You haven't a leg to stand on except "Hickman said...", which doesn't hold any weight considering what Hickman claimed isn't what was depicted in this encounter...which come to think of it, is truly arrogant. He won't admit his creations would have lost otherwise, even though Galactus clearly dominated them before they merged.