That was a problem that Blizzard recognized. Specifically, the weapons and trinkets from DW were way too strong for LFR, even above the loot from Heroic Firelands.
LFR in MoP will not have such powerful weapons available, GC said they are making sure of that. It will be a lower ilvl than the previous tier. And the new loot system, being much more random, will make it very difficult to get a specific piece of gear you want from LFR.
They don´t wnat LFR to be the most viable way of gearing up, but a way for casuals to see content. Of course, some gearing up will come from it.I myself will run LFR a couple of times trying to find some better pieces at the beginning, but later I'll go to normals and never look back.