It sounds a bit counterintuitive, but simply being unbeaten is not an absolute measure of success. Just ask New Zealand.
At the 2010 World Cup, New Zealand tied all three matches it played and promptly went out in the group stage. It was the only one of the 32 teams in the competition not to lose at least once. Even eventual champion Spain dropped its first game before rolling off six straight wins. Being unbeaten sounds great in theory, but it isn't everything and it doesn't always tell the whole story. That's as good a way as any to assess the landscape across the nominal top five leagues in Europe.