Composite textures, that’s it, thanks!
Composite textures will help, you can see in the documentation how both temporal AA and it make a shiny but rough surface darker. But Dethrey is right, for far away lanscapes there’s still going to be a problem. Right now I don’t what to do about it either, far shadows with a large number of high res cascades and making sure lods are extremely high/distance field shadows… but all that sounds expensive.
I’m afraid better than that really would need Epic to add more features, as far as I can imagine it at least.