I understand and I agree - the visuals should support the gameplay. Visual cues (cliff = unwalkable) and supporting the magic circle (holding up the illusion of the game / experience) are critical components of that! In that sense Mellow Shallows is a terrible example overall - there are no cliffs and those that do exist are walkable , haha. That was part of the original map however, this is just a remaster.
Everything that you mention (thank you for that) is certainly possible with the techniques I use now! It really helps with understanding where to take things to - right now the world machine file is quite basic and it can do with various more masks to communicate various pieces of information (visual cues such as cliffs, shores, elevations via color coding, etc).
So in this case - the cake can be made and eaten .
I'm experimenting next on a LOUD map (another Supreme Commander community) that resembles springtime (melting snow) - I'll try and 'encapsulate' this idea of visual cues in that map. Once that is done I start with a map for Sanctuary.
(edit) As an example with a different style:
Rainmakers with (top) and without (bottom) a map-wide normal map
The visual cues are not 100% incorporated here yet - I'm working on it all .