As long as World of Warcraft has been around, there has been a very obvious divide between the usefulness of ranged DPS against that of Melee. As early as Molten Core, the distinction was obvious. The fact that it was often limited to a single melee group shows that there has never been a time when melee DPS is as favourable as ranged.
Even now, while mostly doable with any composition, there are still times when the melee heavy raid setup that my guild runs with struggles, and Warmaster Blackhorn heroic is close to impossible. (At the time of publishing, Blackhorn had just gone down, but only due to switching to a ranged heavy setup, that was vastly undergeared compared to the Melee mains.)
The only time Melee DPS is preferable is Asira Dawnslayer in the Hour of Twilight. There seems to be a lack of design ideas forthcoming from Blizzard concerning how to incentivise melee DPS, without making ranged completely redundant.