When you go into the world editor, select terrain paints, then terrain material editor. In there it asks if you want to convert to pbr. Then you have to update all of the files (ao, normals, etc.).
that's my question, how do I do that? I'm seeing basetextures used rather frequently with the official maps, is that important?
It is. If you take a look at east coast the devs use the same base texture files for each terrain material. The devs use a nice made 2d drawing of the whole map as base texture. Why is that? In game the terrain is then painted with the color of this base texture according to the terrain material used. This technique has the negative side effect that when you start paint asphalt terrain on grass the asphalt is green because of the premade file of the whole map. I guess if you would use dedicated base texture files with only the plain color of the terrain the painting would work nicer and in the end you could use the technique of the devs. What I do: I export the terrain in World editor. Then I link the exported terrain images as layers in photoshop. In a mask layer for every layer I fill the white areas with an according color for the terrain type then I have a generated base texture for the whole map. I save it in color and desaturated in greyscale With the materialize tool I generate normal and AO texture then link them in material.json. works quite okay. perhaps I make a tutorial video the next days.