I thought Norse gods did dickish things too. Wasn't there a legend where Odin punishes the world when his wife steals a part of a golden statue humans built for him?
that particular legend was written as part of the
Gesta Danorum, which also claimed that Thor and Odin were merely cunning sorcerers that tricked the people of Denmark, Sweden and Norway into believing they were gods, so I'm not certain that's the best legend to use.
Plus some interpretations say only worriers get a pleasant afterlife and the sick and old get left out in the cold so to speak.
It was a rather nice place in the original myths, but once Christianity started to seep into thing, that's when Valhalla turned into a glorious place to live, and Hel was merged with the Biblical Hell.
Remember that Valhalla was originally intended for only the Greatest and most powerful warriors to go to after they died, and Hel was for everyone else.
Normal people weren't punished.
IIRC Fenrir wasn't malicious until the gods chained him up. And the only reason they chained him up in the first place was because of the prophesy that he'll kill Odin. So by by betraying Fenrir (they told him the chain is to test his strength and that they'll release him if he won 't be able to break free) and pissing him off by keeping him on a leash till the end of time they created a self-fulfilling prophecy. So yeah, Fenrir character is not one-dimensional "big bad".
Quite honestly, given how often the gods came into conflict with the Jotun, and his parent's aren't exactly the best people...we could see a different legend come out of that, that ends with Fenrir being killed Thor or some other god.
So was Set, and yet he evolved into someone Egyptians worshiped.
As for the constant "Set went from hated to worshiped" that's ignoring what happened.
Remember that Set was the god of Storms, Foreigners and Deserts. When the Hyksos took over, they found Set to be very similar to their chief god, and made him their new head god.
Fenrir, on the flip side, is never really fleshed out, so it's unlikely that he would be picked up and combined as Set was.