Hi there!
I have tried some "World Studios" along a couple of months. Instant Terra was the most suitable tool that I have seen!
but it is missing an important feature that there is present on WW3.
During my research I found the youtube's video
https://www.youtube.com/watch?v=oaM1NAoCzSs that is a tutorial to export Instant Terra maps to UE4, when the author import them into UE4 the landscape looks so flat, guessing a proper Z Scale sounds bad!
WW3 does unit's scale converts
note that WW3 hints the suitable Z Scale to use on UE4 import, it would be amazing see this feature on Instant Terra!