I'm not convinced it's a terrible rule. There have been some examples given of difficult situations, but there are ways around those situations. In FrankHTown's example on the trap, if you know Team A has the ball, and you turn around to verify it's Team A's coach calling the timeout, blow it dead and sell the timeout. If B stole it in that fraction, they are not going to complain too much if you sell the call and explain it why it was granted. Also, where's your partner in this instance? Your partner needs to be aware of the possibility of the TO and to watch for it if the trap is in your area.
Taking away the coach's ability to call TO will not necessarily fix this either. As you're focused on the trap, or 5-second count, what if the coach tells one of his players to call timeout, and that player is not in your field of vision? You or your partner still need to know it's the team in control asking for TO. And that could come from anywhere on the court. At least you know where the coach is (approximately
) so it's easier to be aware.