Jebb had a few injury problems that kept him from performing on his loans. In the end, his development just stagnated. He's a talented player, but the big issue is that there were/are better and arguably more promising players than him in his position. I feel if he stayed fit on his loans, then it may have turned out different for him but it was always going to be difficult.
He can still carve out a career for himself IMO, if he can stay fit.
Similar thing happened this year with Brooklyn Beckham's short-lived stint here. By all accounts, he is a talented player - but apparently he had better players in front of him at U18 level.
Jebb was involved in an incident where he racially abused another player. That couldn't have done him any favours, we're a classy establishment here.