>>49173252As
>>49177171 said, the problem is less Aggron itself and more just the rock type in general. It makes almost every type significantly worse and the potential trade off of STAB coverage isn't remotely worth it since every Rock type move either has no power or no accuracy. The best way to buff Aggron would be a significant change of the rock type to make it more balanced.
Since that's unlikely, here are the easier but still significant ways to buff it
>Increase Head Smash's accuracy to 100%, I should not need an entire ability and entire item to make use of just one move>New ability to turn fighting weakness into an immunity, like a flash fire for fighting. I can buy it falling over because of the ground, but punching a steel dragon should hurt your hands>Since it was Tyranitar's foil in X and Y, give it a BST to match Tyranitar 