I think the only reason that Cotonou is counted and Valparaíso is not is because Cotonou is the largest (and probably best known) city in Benin, so it's better to explicitly state that it's not being counted as a capital.
Cardiff's as valid a national capital as Crayola.
Have a little, faith. It is NOT weird to have knowledge and (like to) learn stuff. yes cheaters exist and sadly are on this site as well, but I think a much bigger part are the nerdy type (in a good way!) that like to test and broaden their knowledge.