Upon further investigation the problem exists in the editor as well, but the effect is not as noticeable when the camera is still (things that move in the distance like swaying trees still shimmer when the camera is still, which makes sense), and unlike during gameplay where the camera moves with the player character during the idle animation, in the editor the camera is completely motionless without any user input

It looks like this is a side effect of an intended feature, where when the camera moves close enough to the ground, the range of the depth buffer changes, or perhaps it becomes logarithmic? Presumably this is done so objects very close to the ground don't z-fight, but objects far in the distance suffer as a result. I must admit that in my testing in the few spots where the infantry camera could be tricked into thinking the camera is far off the ground while still standing on it, I haven't noticed objects close to the ground and terrain struggling with z fighting, so an option to disable this automatic change in the range of the depth buffer so objects far out render nicely would be welcome, or at least an option that considers the object render distance regardless of camera altitude to the ground