Centre backs are one of the hardest positions to judge as how good they are entirely depends on the style of football they are asked to play.
People raved about
Michael Keane - who when asked to do anything but very deep defending and shot blocking looks terrified.
Benitez and
Moyes play systems that are great for centre backs. Two banks of four, force teams to go out wide and cross and head away the chances.
Mangala was a £30m signing and talked about as a guaranteed star and now looks shot.
Zouma played 20 times for Chelsea (practically every game until he did his knee) when they won the league a few years back, winning the league cup final playing in midfield. Then played in a chaotic defence under Hughes where everyone looked dodgy, when the new manager came in and organised things he looked really good again.