In the Marvel Cinematic Universe, the lightning ax Stormbreaker is more powerful than the magic hammer Mjolnir. Even so, Mjolnir still has some unique points that Stormrbaker does not have.
1. Mjolnir cannot be raised by those who are not worthy
This is the main advantage of Mjolnir over Stormbreaker. In the beginning, Mjolnir was also not under any special enchantment. Later in Thor 1, Odin “understood” Mjolnir so that the hammer could only be used by those who were worthy. If the hammer lifter is not worthy, not even the Hulk can lift it.
And Stormbreaker until Endgame has not been given a similar charm. So even the bad guys can use it, Thanos even attacked Thor with the Thunder God’s own weapon.
This worthy charm is not only useful for protecting Mjolnir, making it invulnerable to Thor’s enemies. Thor can also use it to thwart humans or enemies. Take for example Thor’s actions in Thor: Ragnarok. While in Muspelheim, Thor placed Mjolnir in the dragon’s mouth. The dragon had fallen and it was difficult to move.
In short, only those deemed worthy of the Mjolnir hammer can use it, but this same rule does not apply to Stormbreaker.
2. Mjolnir can make others have Thor’s power
This is also another unique feature of Mjolnir. Those who are worthy to lift Mjolnir will have the power of Thor. When Odin banished Thor from Asgard, he kept Mjolnir with him and cried out: Whoever wields this hammer, if he is worthy, will possess the power of Thor. Meaning that if the hammer finds someone worthy, that person will be able to use it, regardless of physical strength.
This was demonstrated in Endgame, when Steve Rogers was able to use lightning attacks with lightning while holding Mjolnir. This is an interesting ability that can come in handy if a worthy hero other than Thor needs a boost to fight enemies, for example.
In addition to receiving the power of lightning, Mjolnir also seems to be able to increase the physical strength of its wielder. Steve Rogers has been buffed using Mjolnir. Steve’s increase in strength may not be so pronounced, as he is already a Super Soldier. But there will be many other cases where it becomes more obvious. Jane Foster looks to get a buff next time she uses Mjolnir in Thor: Love and Thunder.
3. Historical factors
The uniqueness of Mjolnir compared to Stormbreaker is also historical. Stormbreaker is still fairly new in the MCU. This weapon was only created in 2018, during the events of Infinity War. Meanwhile, Mjolnir is an old weapon. A hidden mural in the Royal Palace of Valaskjalf shows the hammer used by Hela when Odin and Hela conquered the Nine Realms in the past. That is, the historical element of Mjolnir is also stronger than Mjolnir.