Hello, author here.

It's actually more efficient to do a hybrid approach, especially at high view distances. Rasterizing triangles is extremely fast, and is basically a perfect primary-ray intersection. Ethan Gore recently did some experiments with raytracing and said that for large scene volumes (his engine comfortably renders the entire 32-bit range, or 4B^3) it turns out to be faster to do raster for primary rays and raytrace shadows/GI.

I've always wondered why voxel engines tend to produce output that looks so blocky. I didn't realize it was a performance issue.

Still, games like "C&C: Red Alert" used voxels, but with a normal mapping that resulted in a much less blocky appearance. Are normal maps also a performance bottleneck?

It's way more performant though and looks fine so I see the reasoning why you would do rasterization instead