Earlier quoted context omitted.
Spaniard; can confirm. 3 hour breaks are simply mandatory for small shops. In the south of the country during summer there is literally no way you can go out until... 19 or so if you don't want to die. So if shops closed then, there would be no business.
Small shops manage to operate in, say, Arizona during those hours. That said, I think Spain's hours are a more natural adaptation to the climate than Arizona's.
Personally speaking I've never seen much value in living by the clock if it puts you in conflict with the seasons. The notion that people everywhere should adhere to the same schedule regardless of local conditions is inherently absurd.