Sorry Phemox ,
but i prefer powerfull workflow :
writting shaders each time i want a layer for terrain .... pfuuuu ...

in BV engine it detects how many layers you have loaded and do as many passes
as layers you have :

NO MISSING TOOLS TO CODE.... sorry , but when i use BV (it could be Torque also)
i have a panel for terrain editing incorpored in the editor like with F11
on Torque qith all things we need !

3DGS could do that and that ... ok , but for people wanting to make 2D/3D art for the game and script only ... it's very very behind for terrain

Now yes you could use irrlicht , ogre3D , or 3DGS and code lot of complete tools
How many time will it take ?

if you like coding ok , if you hate coding , and prefer only to od game logic
that' s bad to hear : "write or modify that".

well let's wait for 3DGS to evolve !