Interestingly, one of the more OP aspects of earth magic is increased gravity. Specifically, and this is one almost NOBODY ever thinks about, is using increased gravity as a buffing effect.
Basically, this goes down to how people started bashing on oversized swords a while back. Super strength is not enough to let you swing around an oversized sword, because the torque generated by the swing would take you right off your feet.
This effect can be compensated for if you increase your own weight. If you weigh more, you can swing around heavier objects as you use them as weapons. Imagine bringing a tree-size sword to a fight and cutting down an entire formation at once.
This is one of many things OP about earth magic.
Another one would be attacking enemy infrastructure. When it comes to warfare, breaking the enemy's roads, water-lines, power-lines, bridges, walls, and military fortifications is something that can turn the tide of an entire war effort.
Now, all 4 elements have ways of demolishing these things. However, earth just so happens to be the most efficient for the job, putting in the least amount of effort for the greatest result. It can take down enemy infrastructure over the widest scale at the fastest speed while expending the least amount of energy in the effort.
Also, if you are going with making gravity an advanced form of earth magic, and you also allow it access to the ability to reduce gravity, reduced gravity magic can actually be used as another way to un-foot your opponent. This is just as counter-intuitive, but it makes perfect sense when you actually stop to consider it. A lot of people tend to think being lighter means it's easier to move around. But, it also means it's easier for others to move YOU. So, reduce your enemy's weight. As soon as you do that, their attacks will no longer do as much damage to you, but anything you do to them will blow them away like you are blowing away a feather.
It will make your opponent practically helpless. And, it would be quite the way to mess with any of the self-propulsion methods
@Zirrboy mentioned the other elements could employ. If their weight suddenly reduces but they haven't reduced their propulsion, their flight will suddenly become very unsteady. If it's one of those magic systems where you have to concentrate, being hit with a low gravity spell could even be enough to disrupt your spell in progress.
(Also, high gravity as an attack would be effective, but as a trope it's an attack method that's defeated almost 100% of the time by the grit and determination of the person being targeted by it. It's an uninteresting method of attack, and very predictable how it's going to be defeated, so it's recommended not to use this particular method in your writing.)