There is no evidence that Gorr would defeat Darkseid. Darkseid's Omega Beams could erase Gorr from existence, time displace him or even send him to an alternate reality. Hell, Darkseid could even resurrect Gorr after killing him and then kill him again just for fun. Darkseid is not a run of the mill god, some nameless, no backstory shmuck. He is the ruler of Apokolips, has GENIUS LEVEL intelligence is immortal, and has gone toe to toe with Silver Surfer and Galactus in the same day! DARKSEID IS!!
Gorr rips Darkseid's head off with ease.