Currently Online 
The famous comparison which really highlights what people are talking about when referring to diminishing returns
Obviously an untextured, fairly undetailed mesh has it limits in communicating the point, but back in the day a generation leap meant immediate and obvious ways of making night and day difference to a character model, to a texture, an environment. That doesn't apply as much anymore.
You won't suddenly get a hugely noticeable difference by doubling the polys on Ellie's character model or increasing the texture detail. The scenes are already populated to a degree that feels authentic, doubling the number of meshes within the environment won't suddenly make the game more believable. The rendering techniques on skin and hair & pretty much every texture is already are very close to objective realism. The baked lighting is amazing and doesn't need raytraycing to make the scene fully convincing.
