He has ended up on the bench cos he has been getting injured
Don't be so ridiculous, man. Injuries have only been a problem for him in the last year, prior that he's was relatively robust.
aye and that is why the seasons prior to that he played 27, 31 and 27 league games - so he didnt really end up on the bench "because of his inability to learn"
Souness, Roeder, Allardyce and Kinnear generally picked central defensive partnerships that didn't include him. Roeder had him mostly at FB, Kinnear quickly discovered that he wasn't up to it, as did Souness who even bought Boumsong because of it. Allardyce had him 4th choice behind Faye, Cacapa and Rozenhal.
They can't all be wrong. Hughton only started him last season because there was no alternative.