Okay I see, it's still not going to save godzilla.
Well what the hell is gozilla gonna do to stop it? If he tries to fly to him, Goku will just IT away or fly away, or just run the same way he did kefla, the same if he shoots atomic breaths, Goku's mid air maneuvers and acrobatics plus IT is the whole reason why he claps an opponent bigger than him in a fight, he also has experience fighting dudes bigger than him.
The level of power cell was using was still above Goku's so that's not a point.
What are you trying to say that bigher blast= weaker blast? Do you know how wrong that is? Well okay whatever then, take this example of a vegeta significantly weaker than the Goku here fighting THE SAME perfect cell, he charged up his final flash. Cell was like, hit me bro. And when he shot it, cell was FORCED to dodge, had a chunk of his arm and body NUKED, and this blast was so massive it was comparable to the size of the earth. Now this is a stronger Goku, what is stopping him from doing the exact same thing? It's not like that's his only win condition, that's just one of many.
Yeah the off guard thing does lower durability, but doesn't apply to cell here, since he was fully expecting the attack to come from above but it came from below which means he was only caught off guard in the direction of the attack but wasn't suppressed. This is also supported by how a far weaker vegeta was able to vaporize a cell that was 180 degrees away from being called off guard.