This is an incorrect hypothesis. The other methods of taking relief from an unplayable lie do not guarantee you a good lie. Even relief from obstructions or GUR don't offer any such guarantees. You might get a good lie, but you may also be required to play from a spot equally as bad as where the ball currently lies, depending on the situation.
Sometimes there is no good choice, no matter what option you choose under rule 28. If you play a stroke from the woods trying to fit the ball through a 2 foot wide slot, then hit a tree and bounce deeper into the woods, your best option is to replay that stroke (stroke and distance penalty), yet aren't guaranteed that the ball when dropped there won't bounce or roll into an even worse situation. You could literally be in a situation where you would have to carefully chip the ball 3 or 4 times to get out and be able to post an actual score for the hole. In a stroke competition, this is what you would have to do or be disqualified.
Relief from GuR or an obstruction only allows a very specific dropping area based on the location of the ball and the nearest point of complete relief. If that puts you in bushes, or 2 foot rough, or embedded stones, then that's where you drop. You don't get the best point of relief, only the nearest.
To say that you are always guaranteed a good lie when taking relief anyplace except in a bunker is clearly not true.
Well stated Rick. But relief from a bush or water hazard will almost always give you a better lie than inside the bush or water hazard. GUR and obstructions are a bit different because I am not declaring the ball unplayable. Rule 28 Part b seems to be the fuzzy point for me. If I am in a bush or water, I can go back with no limit. Perhaps, if they eliminated part b, then it would be more consistent with respect to bunkers and other hazards. If I am allowed to go back any distance, I can most likely find a spot for a better lie.