Terrain wise, if hovering units can't climb steep hills, or work in overly soft ground, there are considerations to having technologically inferior, but tactically useful modes of transportation, including wide track vehicles and spiderbots. Bipedal would never make sense since these aren't actual people driving them. Gravity channeling could require a firm, relatively flat surface, and make room for numerous alternative applications.
The third faction was stated as not using the same technology for transit a while back too.
Well, I can see how a steep hill wouldn't be easy, but the soft ground would work better for a hovering unit. Like, just floats over the ground while something else could get slowed or even stuck.
We haven't really seen the hovering capabilities as far as I know, like can they hover over water? If so then swamps and mud shouldn't be an issue. As for hills, do they hover by pushing from the ground under the tech or from the gravitational center? If its from the ground under it, there should be no issue with even being upside down since it 'attaches' to the ground under it rather than the gravitational core (planet core)
And please do tell about the third! Can't wait to see