Aggron: Good for anything?

I like to use him as an opener in PvP. With his wide array of resistances chances are good that you will end up in a favourable matchup, forcing your opponent either to switch or take his lumps. Aggron has high stamina and can thus wave the shields in most cases. Thunder helps him against water opponents, at the least making them use up their shield supply. At the best, after an initial Heavy Slam the opponent decides to forego a shield - and gets hit with Thunder to the face. Dragon Tail is enough protection against most fighters, which have low stamina. For the rest, you have to switch. I team him up with Gardevoir and Kyogre. Having only one bar moves works for Kyogre in this team, as I use Aggron to waste the opponents shields.

Aggron seriously needs some new moves

Aron are easy to find weatherboosted in many areas, so Aggron's niche is maybe a budget steel-type for Ultra league (Lairon is better in Great) and a budget potion-efficient gym attacker.

I remember actually using Aggrons for a gym early last autumn because the fight to get first gold was so intense I was running out of healing items and had to resort to a team of potion-efficient attackers instead of Machamps. But that was before MM Metagross.

He's great for a couple of things, but probably the best is when you're at a traffic light and won't have time to take the whole gym.

Yes! It has Dragon Tail, which is super effective against dragons while being resistive to them. Worried about water? Give it thunder!
It's pretty versatile. Recommended for ultra league only.