Otamendi has always been error prone. The goals he scored last season and some of his performances in bigger games lead to a big increase in his value. He isn't light years ahead of that player that was loaned back to South America from Porto. He's still our best bet when Kompany is out, and once Kompany is back he will compliment him really well. Most modern day defenders are error prone because they try to be really aggressive and intercept rather than tackle. I also think defending is all to do with the system. Most teams who sit deeper look better defensively because they are compact and have bodies behind the ball. Most teams who play high look the total opposite. We try to emulate Bayern and Barca with their high line, but they know how to win the ball back without needing to involve their centre backs. We don't.