They added a new move to the game that actually helps heavier pokemon. The move is called 'heavy bomber' and it apparently does more damage depending on the weight of the pokemon using it. I can easily see this replacing gyro ball on a lot of steel types.
Pumice stone Nattorei to survive Kabutops low kick and OHKO back?
Pumice stone swampert surviving grass knots?
I think there are some niches. Just like shed shell.
Iron Ball.
It won't. I don't remember if it maxes at 100, 120, or 150, but it's based on botht he users weight and the targets weight. In most cases, the difference needs to be significant for it to max damage, and won't max on most of OU. Gyro ball is much better, especially since one could even run scarf deo-s to beat dory and swift swimmers now.