I just had a go against 6 Adaptive AIs and the constant stream of bombers can make it an impossible task. I had to use a trick to get rid of that problem (and then it's very doable). Anyway, the pathfinding is decent. Good for air, but the AI really struggles with the small gaps, you can see loads of units clumped together at those narrow mountain paths.
It's a bit better in the lower parts of the map, but the choke points here are wide enough to let small armies pass.
Air units and air drops do a very good job though. Especially the drops.
One more issue: some mountain paths look like they're too steep (cliff texture) but units don't have that many problems moving over these ramps.