In some respects the current rule is better than others as I think it is " there must be no doubt that the beaten horse would have won the race". ie if there is any doubt, the result stands. The main problem is when the beaten horse was definitely prevented from winning the race but didn't manage to finish second as a result. I hear that the connections of Golden Horn considered themselves very lucky to keep the race at Leopardstown where Free Eagle was nearly knocked off the course and finished 3rd. Had he finished 2nd it would have been a different story.
Re the St leger, if the stewards had applied the rules to the letter, based purely on the video, they would not have reversed the placings. I believe the jockey won it in the stewards' room and that is what shouldn't happen.