For control decks, losing the ability to exile your own creature is a minor nerf, but it's an edge case. Usually you'd want to exile your own creature to drop something like an Arrest or Stab Wound, but it's best to do that when you have a flicker or bounce effect to get the creature back into play (in which case, you could flicker or bounce the creature in the first place).
The power/toughness change is more important. Banisher Priest fits a little better in the aggro deck, but is significantly worse against aggro. It can remove one creature, but can only trade with two-power creature (unless it has first strike, which is quite common). That makes it more of a tempo play. Fiend Hunter is a better stabilizing play, since it can block a two-power creature indefinitely.