these are all valid points to bring up if it wasn't already understood that this is a FANTASY setting. Maybe in becoming an Angel, Tyrael had no choice but to bind himself to this sword on a spiritual level and thus can sense where the pieces are. Cain is the last of the horadrim, a group of elite mages with unprecedented powers, so yeah maybe he does have that ability where others don't. It's called suspension of disbelief and if these are what you consider plot holes, I would imagine you are no fun to read, play, or watch any fantasy-fiction book, game, or movie with.