It seems like the primary differences in ground gear armor classes is their gravity resistance (ie, how susceptible you are to topple) and the defense conferred. Heavy armor has less gravity resistance than light armor, so you're more likely to be toppled.

It seems like the primary differences in ground gear armor classes is their gravity resistance (ie, how susceptible you are to topple), the number of upgrade slots available (light armor has more upgrade slots), and the defense conferred. Heavy armor has less gravity resistance than light armor, so you're more likely to be toppled.