I guess your hypothesis is the only way that the player isn't to blame. Played well before large new contract, been pretty average at every club since. Cause - bad management.
I'm sure he got a pretty bad injury quite early on at Burnley which lead to it not quite working out for whatever reason? People often forget that footballers are humans too, and moving around all the time at the age of 18, whilst having to deal with the pressure of being famous must be quite hard.
Played well when surrounded by players playing nice football with us. Didn't play well at Forest who under Billy Davies had a reputation of doing the opposite and hoofing it. According to SM he did well at Boro, to be honest I've no idea what sort of football they were playing when he was there. Did poorly at Burnley who again are a hoof ball team with few flair players. Seems to have started well at Reading too (although was out injured in his last match)