"What if he copied all them all? Would that make him the best ever?"
He wouldn't have time. He's fighting too many people. He'll get over powered and out done. The Fury could match him to a standstill. And the Fury isn't even a Celestial. Imagine what the others could do. Zatanna, Wanda Maximoff, Mad Jim Jaspers, Jenny Quantum, White Crown Phoenix, Dr. Strange. He's not doing it.
Wanda Maximoff defeated Ultron by herself on two separate occasions, one of which she broke him down on a molecular level. But she wouldn't even need to bother with all that. Three words is all it would take, No more Amazo