The problem for me isn't Mangala, yes he makes a few mistakes and hopefully this season will stand him in good stead for next season, The issue is that he is only what 24 years old and is sill what we would consider a young player.
The issue is we got shafted by Porto on his price and paid a premium for a good CB with potential who is not even a full 1st team international player with France.
He as come with a hefty price tag and when that happens you have to hit the ground running straight away with consistency, something that has not happened and probably the consistency side of the argument could be aimed at Pellegrini who chopped and changed the back four nearly every game this year