The bottom line is that Mrrungo Mu is going to squash his opponent, no matter who it is, while Darkseid can hold off either for awhile. Then it's two on one and that's it.
Why would you compare Murrungo to Tyrant? You do realize that Thanos has smiled in the face of the Surfers most powerful blasts, and Millenius took a Surfer board strike to the adams apple, and got up as if nothing happened?
Speaking of the Surfer, he was able to lock up with Millenius for several panels and match power with him. He could never do that with Mrrungo Mu. And Tyrant treated the Surfer like an insect, much moreso than Thanos or Millenius. Still, none of this has anything to do with Mrrungo Mu being able to crush either Millenius or Thanos in combat.
So what? I have the issue in question. Mrrungo Mu made Galactus wary of a fight. Thanos admitted his power is nothing compared to Galactus. And I don't think Galactus would have a second thought about battling Thanos or Millenius.
Mrrungo Mu casually captured Thor and then freed him and dared him to attack along with several other heroes, including the Hulk and Sub Mariner. They were all defeated in seconds and Mu absorbed all of their power! Thanos or Millenius couldn't dream of doing something like that under their own power. Mu is powered by billions of beings, including super-beings. He's in another league.
He was putting effort into. I wasn't very impressed with Millenius. And taking on Thor and the Surfer is nothing that Mu hasn't already done and exceeded. The only way he goes down is if his power source is cut off.
How was Murrungo defeated? You say so what, but the Surfer gave Tenebrous, and Aegis a fight, and they were unable to KO him, while Thanos with the same amount of hits nearly destroyed him.
Mrrungo Mu draws a massive amount of power from a ship larger than Earth. The Surfer cut off his power source and was able to beat him after a battle
The Surfer wasn't doing anything but annoying Tenebrous and Aegis though. The most impressive thing about it was the amount of punishment he was able to absorb and keep going.