I know the subject makes this sound like a cold, hard fact, even though I have absolutely no hard proof what-so-ever, but it's something I've kind of been noticing this entire expansion, and I will detail it below.
It took four different people complaining about this over the course of this expansion for me to come to this conclusion, based on theirs, and my own experiences.
These four are my guild's tanks and healers, with me being one of the tanks.
I remember during heroic dungeons at 90 that I was able to gear my DPS set much faster than my Tank set, even though Tank is my MS and I always queue as a Tank. The same has pretty much held true for most of the expansion, but this by itself was not enough to even make me think something like loot skewing existed.
However, once I started running my Hunter in LFR SoO I started noticing it. My Hunter gets drops way more frequently, and not just drops, GOOD drops. I got a bow on my Hunter in my first LFR Siege run, while my Tank was pining for a weapon for a long, long time, and even then, it was a weapon that lacked Mastery, which wasn't ideal for me. While my Hunter is still sitting comfortably with pretty much full LFR Siege gear, including the AoC trinket and the other good one, I cannot recall the name.
This still wasn't enough to convince me though, it was just something I noticed, and chuckled, that my Hunter seemed to get far more drops, and good drops at that in his runs.
But then my girlfriend, who plays a Priest, also complained about bad loot, or no loot dropping primarily in LFR with the personal loot system, it was only when she started playing her DPS Warrior that she actually noticed strings of good loot drops, and actually getting loot drops period.
Still, I chalked it up to RNG is RNG, because RNG.
Then, recently, my guild decided to reform and come back to WoW in preparation for WoD!
Our other Tank, who is also the guild leader, plays a ton of alts. His main two characters being a Brewmaster and a Paladin, both Tanks. He too complained about what seemed like a scarcity in loot drops while tanking, yet when he leveled his Rogue up, and started running LFR, he was getting drops like crazy, good drops. Had two 528 daggers within the same week, etc.
This is when I started noticing a pattern, it really does seem like loot is skewed towards DPS classes, specifically, pure DPS classes, and less towards Tanks and Healers. Several strong reason for this are that pure DPS classes have no way to shorten their queue times, and are often in queue for a good while, and with Tanks and Healers always needing loot, and not getting it, they are always queuing.
Has anyone else noticed this phenomenon, and how do you feel about? Do you think it's an actual thing Blizzard has implemented? I'm pretty much convinced at this point, and really, I'm kinda ticked off about it. It seems like a shitty way to keep Tanks and Healers queuing.