The 'original sin' is the political over-representation of the nationalist parties because both PSOE and PP have needed their support for the Spanish government most of the time. In exchange of too much concessions, of course.
Or you don't know about Spanish election system or you'r just lying. I think is the former.
There is no over-representation of nationalist parties, there is a over-representation of both majority parties, PP and PSOE.
Almost all the provinces have 3 diputates and the third pary doesn't have any representation.