LFR and LFD exist because in the days before them players liked to lock others out of content. Blizzard could not afford to have a large amount of players locked out so they created this system. A system that NO ONE is forced to use. Yet the screams to have it removed are daily because control was had and it was lost.
Since LFR & LFD a lot of people have gotten much better at playing the game. You can tell that since we went from Vanilla simple fights to the far more complex fights we have now. Without the LFR & LFD systems in place the quality of fights would have to dull over time to meet a population that can no longer practice.