Second best scoring defense in premier league was Arsenal last year.
I'm fairly certain if you ask any arsenal fan how they feel about their defense, they wouldn't be happy about any of them.
Barcelona had the second fewest goals alllowed in La Liga last year too, and their defense isn't exactly top notch.
Lookign at goals allowed is a bit short sighted when evaluating defenses, as if your team can control the ball a lot, they don't have to worry about many chances against.