Sculpting is downgrading

dude wtf it downgrades

Yep, that’s to keep the poly count down. Think of it as dynamic LOD. If you switch to wireframe mode and fly across the landscape, you’ll notice the further you get away from the object, the less polygons it has. I’m sure there’s a way to turn this off (you could just convert it to a static mesh) but it’s there for a reason. If your landscape isn’t going to be very big, converting it to a static mesh would be the way to go.