Since Raiden is one of the most powerful characters in Mortal Kombat, I know that he should be on par with some of the strongest characters in other franchises. It’s not the real reason.
Kryptonians are vulnerable to magic, one of the most greatest weaknesses of them. Since Raiden possesses magical lightning and thunder, he can do vast damage to Superman.
For Metallo, he lacks a bit of focus and intelligence. Raiden is far more wise and is known to be one of the greatest tacticians due to his steadfast leadership in Earthrealm. So, Metallo can be outsmarted and outmatched by Raiden abilities and intellect.
Last, but not least Granny Goodness. She is not as powerful as Darkseid. Granny can sometimes be a little to arrogant, that she can be outwitted by certain fighters. Raiden excels at power and combat experience. So I do think Granny could win over Raiden at some points, but the Thunder God is more determined to be victorious in the end which gives him an advantage.
As a whole, Raiden’s magical capabilities, his godly strength, being faster than how the lightning strikes, and his immense willpower to win, gives him an edge to overcome powerful warriors like those three.
