"Why even have a derailleur hangar? Sheesh. Just build it into the frame."
My understanding is that derailleur hangers that are part of a steel frame or attached to a frame can be straightened/aligned several times before breaking.
Aluminum alloy dropouts and hangers can be straightened a little bit a few times before breaking.
Carbon fiber, no.
The hanger is a 'weak link' that when damaged is meant to fail, instead of damaging your frame or derailleur.