To me he looks more than capable of progressing to be a premier league striker, and a pretty good one. He has great feet, is quick, is good in the air, and like his arsenal goal showed is a cool finisher. His movement looks decent, but a coach will make that better. If I was Lampard I would be wanting to work with a player with those attributes, not ditch him. It is to our benefit.
His fitness issues I would hope can be managed. Our physios will get to know him better, and will develop personalised routines for him. Lots of players have learned how to look after hamstrings as they get older. Sometimes it can be something elsewhere in the body causing it. I am going for optimism with his injuries, and as he becomes more match resilient, he will be less injured. The 4 year deal is because I think he had massive untapped potential, similar to Clarke, so lets protect our investment in his development.