No I don't mean arrogance but he just doesn't have that inner belief that the top top guys have.
Doesn't back himself to get through the toughest matches against the best and capitulates more often than not, he could be two sets up against the better players and end up losing easily.
I also think basing his game off of Fed's has been a huge mistake, yes he plays similar to Fed but its nowhere near as effective. For example his backhand is not great at all, there are so many guys on tour that have a superior backhand like Philipp Kohlschreiber and that shouldn't be the case because for starters they aren't ranked that highly.
Dimitrov doesn't really have a "killer" weapon and it shows in his matches, his backhand in particular doesn't produce many winners and is routinely targeted by the better players. Compare his backhand to Thiem's or even the likes of Gasquet and it's not even close, I think his early coaches did him a massive disservice pushing the Fed comparisons. If he'd developed a game that suits his strengths with a two handed backhand his career would pan out differently, as it is I never see him winning a slam.