What's perhaps not obvious is that if you take a 2006 game and "add" raytracing, there's no relevant information available for the raytracer. Whatever original

What's perhaps not obvious is that if you take a 2006 game and "add" raytracing, there's no relevant information available for the raytracer. Whatever original light sources were used to bake in global illumination does not exist in the game assets used for rasterization. In the best case the original art assets can be used to create raytracing scenes, but it's not as straightforward as it might seem, and most conversions are pretty sloppy. If you want to see what raytracing can do, I'd only look at very, very recent UE5 titles that are designed for raytracing from the ground-up.