So yeah who do you think will win in a 1 vs 1 battle to the death!

Gwyn Lord of Sunlight
From the Dark Souls series he is responsible to the end of the age of Ancients (age of the dragons). Keep in mind that when we fought him at the end of Dark Souls he was already Hollow just a husk a shadow of his former self which is why he was called Lord of Cinder not the Sunlight anymore.

Zeus from God of War series
He was the mightiest of the gods in the God of War series. It took Kratos everything he got to finally defeat him with a lot of help from the Titans and Athena and so many others.

So yeah a fight to the death when both of these individual at their prime and at their strongest form! who will win? keep in mind both of them are so powerful with their lightning spells.