People wank anyone with the title of "God" so much that it's not even funny. It's so ubiquitous of a title. There's no way a god from God of War is comparable to, say, Marvel Thor.
Same thing for immortal. Most of the time it only means "can't die of old age." Surviving multiple stab wounds does not, in fact, make you unkillable.
So it comes down to physical stats and abilities. And Mario has Kratos beat so damn hard in both it's not even funny. Dude can kick castles away, survive black holes, and more.
And abilities? Star power makes him completely invincible (outside of lava and poison), gold flower turns literally anything into coins, double cherry makes copies of himself, and many more. Plus he's shown he can carry multiple of these at a time.
All of this is ignoring the rpgs btw. Even just restricting it to Mario & Luigi games, it'll give him access to dozens of badges and equipment, some of which are completely broken. Bottomless gloves, in probably the most infamous example, lets Mario use any power-up or item in his inventory without removing it.
That's endless amounts of fire flowers, mushrooms, hp restoring items, sp restoring items, stars, etc. Mario could spam each of those to his heart's content.
Mario wins.
