In the last 10 years swimming has seen a significant shift to concurrent type training. As with many sports they realised training the speed out of them and leaving qualities untouched produced very good slow swimmers.
The very good programs (back end) programs have been re-rewarded from the removal of the rubber suits as the drop dead sprinter types from sprint based programs have found the last 15m in a 100m can be a painful journey if the back end qualities aren’t trained.
Its like the 300m sprint…a good male short sprinter and longer sprinter can run fast over 300m…however add on another 100m or 11-12s and then you find out who has done the quality work at the right speeds at race specific ratings while maintaining stroke length.