ArtK78, on 2012-September-27, 10:39, said:
Furthermore, with 5 hearts and 4 spades and a weak hand, responder might have doubled to show both majors. He is more likely to bid spades with 5 spades and 4 hearts since he will be able to bid again to show hearts without increasing the level of the auction. Even then, he might have doubled 1♦ with 5-4 in the majors (in either order) and a weak hand fearing that he needs to be able to show both suits immediately.
Whether or not the practice is flawed, for the reasons you addressed in the rest of your post, a great many pairs are not able to use that premise. The double of a 1♦ overcall is used by them (us) to show exactly 4-4 in the majors. This affects the strength requirements and expectations when opener rebids two of the other major. (Notice I am not using the "R" word).