In a fic of mine, a Hitmonchan was very good against a Steelix, but whatever... I kind of agree that Fighting shouldn't be strong to Steel. Maybe Electric or Water instead... Water types annoy me though.
Anyway, Normal is FAR from underpowered. Some of the best/annoying/strongest Pokemon are normal, like Blissey, Slaking, Zangoose, Snorlax, and Miltank in GSC. Those wily normal types always have tricks of their sleeves.
Grass types get picked on the most. 5 attacks are super-effective to them, and 6 types are resistant to grass (and a lot of those are popular types like flying, dragon, and fire). It's hard to use a garss type against water because water types almost always have ice beam.