The big problem with Superman has always been that he is overpowered. He didn't start that way, and a few attempts have been made to "fix" it, but I don't think they've stuck. Does the effectiveness of the Bat mech suit mean they have addressed this, or does Bats have some special gimmick, e.g. a Kryptonite alloy?
The problem isn't that Superman is too powerful. The problem is writers can't work with Superman's strengths and imagine challenges for him to overcome. Compare Superman to Thor, and all the things Thor's hammer can do. Physically, Thor and Superman are nearly even.
Looking at Mjlonir it has a list of abilities, such as:
Power of flight
Move at FTL speeds
Teleportation
Transformation
Weather manipulation
Casting lightning
Time travel
Energy absorption and reflection
Transmutation of elements and phasing
Healing
and many more, I'm sure.
You could argue that Mjlonir is more of a magic wand, rather than an enchanted hammer.
During the Silver Age, Superman had nearly infinite power, and was essentially a walking deus ex machina. There was no power he didn't have that couldn't get him out of a jam.
While Superman and Thor have both lost a significant degree of their Silver Age strengths, Thor's hammer can still do all the things I've listed, when the writer wants to do those things. Superman has been depowered to "believable" levels (he doesn't have the strength to "juggle planets like they're marbles" anymore and he can't time travel or change the past (seen in Superman TM and various Superman and Superboy/LOSH comics). And yet Superman is still labeled as being overpowered, when a character like Thor is not.
There are NUMEROUS interpretations by various writers who all think they have to depower Superman further to make him relatable or in order to create drama for him. It's a self imposed box, imo, because those stories lack any imagination to challenge the character forthright, or set him on an adventure that would test his mettle. It's thinking like this which has given us scores of Superman origin stories. Because the writers love to wax poetic about what the character could mean going forward, but don't have the imagination to tell stories beyond the origin.
It's a vicious cycle, and I think it's why the character of Superman has struggled for the past 2 decades. No one wants to do the big stories anymore, and no one is committed enough to stay on the project for more than 12 issues (a year) in order to chart out a course for the character. You look at how long people like JMS (The Amazing Spider-Man), John Byrne (FF, X-Men, WC Avengers), Ed Brubaker (Captain America), Walter Simonson (Thor) Geoff Johns (JSA, GL, TT, Flash), George Perez (WW) and Marv Wolfman with Perez (Teen Titans), Grant Morrison (JLA, multiple Batman titles simultaneously) and other stayed on their respective titles and gave it there all. They all stayed on for years, and cranked out some of the best stories for these characters. The last Superman had something like that was in the 90s during The Man of Steel run (most famously Death, Reign and Return of Superman) with Roger Stern (Avengers and Spectacular Spider-Man) and Dan Jurgens (Thor).
