You are right, that many features in game engines cannot be used yet, especially relighting and reflections. But there are cases where game engines (like Unreal Engine 5) are used, for example in Virtual Production with Ledscreens, where a photorealistic background is needed (3d gaussians do look more realistic and are cheaper to produce than a comparable scene made of polygons)

Supersplat is actually a game engine (but for the web)