Each mount is its own mastery track. Like, raptor is a track, jumper is a track, etc. So skyscale is also its own mastery track, which is tied to the living story chapter rather than PoF. The PoF mounts are easier to obtain (assuming you got the expac). Skyscale is a slog to get, but is technically "free" for all.

Only the turtle mastery/mechanic benefits from flat(ish) land, I think. The jade bot mechanic is very general. Fishing and skiffs are if anything water dependent (of which the jade sea has none, despite the name :p). And Arborstone is by definition not part of it. :p

I think they did try to go for a medium in this expac between the pure flat maps of PoF and the pure vertical maps of HoT. How well they did I think depends on the player and their mood/goals. If you're trying to rush from point to point then some of the navigation might be frustrating (esp if you don't have skyscale). If you're taking your time or just looking for lore/ambience, it's very well done.