You’re talking about perfect categories comparing them with the real world.

Diffraction from objects without the loss of energy doesn’t exist, but allows us to solve a simpler equation paving a way to the understanding geometry of the phenomenon.

Real world diffraction is affected by the properties of the material, mostly characterized by linear dielectric permittivity. When you start taking it into account, suddenly the light starts to penetrate into the material, often inducing heat – the primary source of the losses. Equations become messy, but it kinda allows you to calculate things with high precision.