Ever since Sir Alex Ferguson’s retirement 13 years ago, Manchester United have been stuck in football’s equivalent of purgatory and a chastening experience in Hull suggests they could be there a while longer. Michael Carrick’s permanent appointment was supposed to hail a new era at Old Trafford but very little has changed based on this defeat. United were sluggish from start to finish and rightly punished for failing to defend set-pieces with any degree of competence. Centre-backs Semi Ajayi an…