Dimitrov is showing the required choking ablities, now Grigor needs to rise his game up to Roger's level.
As for tie-breaks, Fed had been very good very early in his carreer, far before becoming the player he became in 2004. And you would not praise him this way if he hadn't won 77% of the tie-breaks he played in slams, and 76% in slam finals.
Tomic has also been great in tie-breaks since he started playing with adults (I don't know in his junior years).
Raonic is a player who had not been that good in tie-breaks a few years ago in futures and challengers and has become good one year ago.
Winning in tie-breaks is a lot a matter of self-confidence then it may change along time, we've seen players having very good periods, then very bad ones (for instance Davydenko, Murray), etc ...
But some players have been good from the start : Fed, Djokovic, Isner, Roddick especially.
Anyway, I have the impression that Dimitrov plays a lot of tie-breaks, even when he played challengers : probably his returning abilities are not good enough, and also he has consistency problems (I have also seen him double-fault a lot when I watched him).