To put it in perspective, at this same stage of his career (11th slam entered) Djokovic had already made the semis of two slams, was about to make the final of the 12th, and win the 13th. Harrison still hasn't made it past the second round of a slam and it doesn't look likely to happen in the near future.
Well to be fair, apart from a group of players, it's too much for anyone to be compared to Djokovic. All I'm saying that while his peers(Tomic, Dimitrov, Raonic) has something that they can work on to take them to the top, Harrison pretty much has nothing. I don't know. Maybe he'll develop something. He has time, that's for sure.