I think you're confusing the distinction between classical ray optics and classical wave optics with the distinction between classical wave optics and quantum mechanics. Quantum mechanics and classical wave optics agree on the explanation for diffraction as a path interference effect. In classical optics, the reason you don't see light coming from angles away from the shortest path is because of destructive interference between the other paths.

For example, note that the Huygens principle predates quantum mechanics by over 200 years [1]. As another example, diffraction gratings (which manifestly require interference between different paths) were being made in the mid 1800s [2] but in physics documentaries you never hear of people being confused about how to explain their behavior. Because they are explained by classical wave optics. Also see this lecture which talks about diffraction in the context of ray optics [3].

Where wave optics disagrees from quantum mechanics is in the dim-light limit, when you start resolving individual photons.

[1]: https://en.wikipedia.org/wiki/Huygens%E2%80%93Fresnel_princi...

[2]: https://en.wikipedia.org/wiki/Diffraction_grating

[3]: https://www.youtube.com/watch?v=5tKPLfZ9JVQ&list=PLB1A0BF14E...