Steel beats Rocks and Ice because Metal, when played loud enough, shatters those things.
Steel beats faeries because Metal is the proof of man's dominance over the natural world.
Grass cannot beat Metal, because the sound waves shock the leaves off.
Bugs, Fying, and Normal cannot beat the Metal because all living things stop in awe of the great performance before them.
Poison cannot tarnish the Metal, because the Metal is already on more cocaine than you can comprehend.
Dragons cannot scratch the Metal, because Dragons are incapable of concieving of something more badass than they.
Psychic cannot warp the Metal, because the Metal removes your ability to think.
Rock cannot dent the Metal, for Metal is Rock's pupil that outstripped the master.
Ice cannot cool the Metal, because it just makes a really cool stage effect.
Faeries cannot dim the Metal, as the Metal offends its quaint sensibilities.
Ground Beats the Metal because it knocks over the amps, rendering the Metal briefly powerless.
Fire beats the Metal because it is already really hot and sweaty at a Metal concert, any more heat makes people go home.
Fighting breaks the metal, because a violent mosh pit gets the cops involved.
The Metal used to keep out the Ghost and Dark type edgelords with their Bars and age restrictions, but then they grew up and can no longer be kept out by carding.
The Metal type makes perfect sense as is.