Thor has wielded Mjolnir for most of his time in the Marvel Cinematic Universe. In his first self-titled film, Thor’s journey involved his development from an egocentric prince of Asgard to a hero worthy of the magic hammer, but in the movies since, he learned the hard way that his power came from within — not some shiny weapon.
Mjolnir is purported to give Thor strength, but after retrieving it during Avengers: Endgame, the God of Thunder can't stand up to Thanos in their final confrontation — even though he more than held his own in Infinity War. The obvious explanation is that Thor isn't at his physical peak during Endgame, but a new theory offers an even more compelling explanation for what went wrong.
Reddit user brownpanther_333 suggests that Mjolnir actually dampens Thor’s powers and stores them for itself. The theory's main piece of evidence is that the Avenger was much more powerful when he was without his hammer in Thor: Ragnarok and Infinity War.
By comparison, Captain America who was able to draw lightning from Mjolnir in Endgame, while Thor could barely muster the same effect. So what gives? u/brownpanther_333 thinks that Odin may have installed a dampener to absorb Thor’s power to keep him in line, fully intending to gift his son with Stormbreaker when he became less brash and self-centered.
It’s true, Thor has been without Mjolnir before — be it after Hela destroyed it in Ragnarok or when he wielded Stormbreaker against Thanos. In both of these instances, he’s able to draw upon the power of lightning to thwart the enemy. Thor is at the height of his power at the end of Ragnarok and unleashes a spectacular display of electricity that takes out half of Hela’s soldiers. During Infinity War, he similarly wipes out a large army and nearly kills Thanos with his lightning strike.
In Endgame, however, Thor is a shadow of his former self. One could argue that the five years following Thanos’ snap has left him reeling and feeling unworthy again. However, when he finally does rise to the occasion in battle, he still isn’t as powerful as he was before despite the fact that he’s wielding Mjolnir once again.
From a narrative perspective, you could argue that Thor was made weaker to show off Captain America’s strength with the hammer. Either way, the theory certainly goes a long way to explain why Thor gets tossed around so easily by Thanos in Endgame.
The Inverse Analysis — In Thor, Mjolnir works a bit like the sword in the stone. Thor must prove himself to obtain the power he lost, unknowing that he had that power all along. However, it seems that his overreliance on the hammer may be unfounded, and it’s hard to overlook the evidence of how powerful Thor really is when he isn’t wielding it.
We also know Captain America returned Mjolnir to the past at the end of Endgame, so it’s possible Thor will solely wield Stormbreaker (or the battle-ax Jarnbjorn) in Thor: Love and Thunder. Without his first hammer as a crutch, the God of Thunder may finally be at his most powerful yet.
Avengers: Endgame is currently streaming on Disney+.