PBR algorithms tend to at least start from the rendering equation and simplify/approximate from that. They attempt to maintain some semblance of accuracy by eg.

PBR algorithms tend to at least start from the rendering equation and simplify/approximate from that. They attempt to maintain some semblance of accuracy by eg. employing the conservation of energy of emitted vs. received light of every point of the scene; or expressing matte texture by the statistical behaviour microfacets of a rough surface; or using actual radiometry/photometry units to express lighting elements of the scene; making the scene also be expressed in concrete real-world units, ... There's still a lot of cheating and smoke and mirrors, but at least all these operate from the idea that the math should check out. This is in contrast to more oldschool approaches that were fully dependent on tweaking things until they looked right - ie., taking blinn-phong in a scene with some 'ambient lighting' and operating in fully imaginary units, modified by an artist on scene-by-scene basis.