Um, source? He never killed Zeus, Zeus tripped on a magic landmine created by the Unknown Entity and died for all we know.
Doesn’t mean much because they all beat his ass 0 diff
Arthur still fought and beat Undead Poseidon, also Durza has been stated to be able to AMPLIFY the powers of his Undead Gods too, so ur wrong 
Proof? zero mention in lore doc, only thing Prometheus did was beat an old man. Weakened Theos = Weakened Prometheus, therefore prime theos = prime prometheus.
At least they actually DID something with their powers instead of being a bum like him and getting carried by magic Unknown Entity 