I thought any mistakes in any deck would usually cost you the game?
But once you've played the deck long enough, mistakes will lessen, and you'll learn through those mistakes (no double clerics vs priest, no chillmaw when you have board control, Voljin the Ysera and wipe her off (12 hp!), careful with heal when you have Auchenai, no more than 3 minions on board everytime… stuff like that)
Not going to argue on that, Dragon Priest has a vast variant of decks and play style, I’ve probably changed my DP deck more than 10 times to find the right one that fits my style (and it’s still on going). I guess it’s up to your play style, I have a copy of each Cabal, Shrink, and entomb in my current deck, so it’s flexible in that sense, depending on which card is drawn.

Usually I’d Cabal + Shrink more for removal than actually wanting a copy of that minion, just have to be wary of brawl, that’s 3 cards on board including the Legendary u stole, excluding the existing board minions. I usually stick with the rule of 3.