>>52514237Aggron should have been Steel/Ground. Comparing the defensive typings of Steel/Rock and Steel/Ground. It just isn't fair.
Even though Steel/Rock has a quad resistance to Normal and Flying, those are primarily physical attackers, so just resisting them is fine enough. And while you would get a weakness to fire as a result of being Ground. A Steel/Rock has two quad weaknesses to both Fighting and Ground, which are the two best attacking types in the games.
A quad weakness is already really hard to work with, but two is suicidal. Which is why Mega Aggron was so good just becoming pure steel since Aggron was so bad defensively.