You shouldnt be using “landscape splines” - no one really does since they do not work.
What you should be doing is creating splines, then using a bluetility call to have the landscape deform and paint a layer of that spline (or any other).
Your pcg can likely just avoid the spline since you can tell it to consider (or not) the actual spline.
On top of that, usually the same spline is used for navigation - which isn’t possible with landscape spline.
Additionally, since no one making a game who cares about performance even just a little bit is going to use a landscape on the final build - even landscapes are something you shouldn’t really use…