It's got to pretty corrosive on Paddy's self belief if a "legend" has a personal vendetta against him making it as a footballer. If I was 20 and some industry legend went public telling everyone how shit I was it would probably have smashed me. He's really just a flippant prattler with no regard for anyone else but Dermot. He's known for doing absolutely no research for his commentary or media roles and for forming strong opinions which he stubbornly backs. It's a pathetic stance on kids career as such and makes me see him as an enormous campaigner.
There's no doubt that it must take some toll, but I beleive Paddy has enough gumption to be able to look beyond it. His personality that is shown in the public eye seems to be one of a relaxed, but self confident young bloke with enough intelligence and good humour to work past what others say and think of him.
The bloke must have known (if not have been told) he was good enough to play the game at an elite level from a early age and those around him would have set him up to be realistic about things like copping flak from previous champions of the game.
It's not as if he is alone on his journey, the club would have been working with him very early on about structures and procedures to handle any pressure whether it be physical or mental.
I'm getting a bit tired of reading about DB on this board. He really isn't worth mentioning because like you say the bloke is a stubborn, unprepared tosser that will do anything to try and remain relevant and obviously has some deep seated issue with the club.