First off, it feels like most people see that Snorri Sturluson was Christian and immediately assume he did what the Irish monks did to Irish mythology. This completely ignores why he wrote the myths down, which was to establish a cultural connection between Iceland and Norway, in order to try and get Iceland to join the Kingdom of Norway (which failed). It also ignores that fact that he WASN’T A MONK. Outside of a part about the Aesir being Trojans and living in Asia (which makes no sense when looking at the rest of the Edda and the myths within), and some stuff about some great god who is more powerful than all of the Aesir and is never actually named, there isn’t much evidence to there being large post-Christian changes.
The second problem is that the theory focuses too much on Loki. He doesn’t do much during Ragnarök. He captains a ship (whatever that meant to the Norse) and he kills/dies to Heimdallr. Each of his kids from Angrboda does more. Fenrir eats Odin, and in some versions also the sun, moon, and stars. Jormungandr floods Midgard and poisons the sky, along with killing the strongest of the Aesir, Thor. Hel(a) brings an army of Draugr from her realm to fight Odin and Freya’s einherjar (Freya got half of those who died in battle). I agree that Ragnarök is a story of revenge, but its not Loki’s. ITS THE JOTNAR’S REVENGE. Revenge for a long list of insults and grievances that started with the killing of Ymir during the Voluspa by Odin and his brothers. Also, both Fenrir and Jormungandr are getting revenge against the gods they hate most, whom they are stated to kill. In the end Surtr, king of Muspelheim, kills Freyr, destroys Asgard, and burns all of the worlds (which since they are made of Ymir’s corpse, make this technically Ymir’s funeral pyre). Also the Jotnar on Loki’s ship aren’t his troops, they are led by a different Jotun, and it isn’t even his ship.
I could do an entire other post on the problems with how Loki gets viewed through modern lenses, and I’m tempted to.