First off, this is not at all a problem in PvP, due to the personally specific, non-random progression of gear. This is only a problem in PvE. Secondly, the only gear slots in question are: head, chest, wrist, hands, waist, legs, and feet. All the other gear slots have other class/specs to compete with.
In PvE, there are several areas to consider. Leveling (quest rewards and dungeon drops), gearing up (5man heroics) and raiding. (This is mostly speculation)
I argue that rewards while leveling are not insignificant. One of the major reasons I am not leveling my Pally with a Holy spec is the low rate of intellect plate in leveling content, combined with a lack of intellect plate helm or chest heirlooms. After poking around a bit on forums and blogs, it seems that many people consider keeping a decent Holy Pally set while leveling near impossible.
While grinding heroics for the latest gear, I imagine the prelude to raiding gear issues must set in. This is where Holy Pallys are guaranteed no competition other than ninjas, (which I assume is an added headache, but I digress). Drops are limited to the combined loot tables of a short list of bosses, but are partially alleviated by quest and vendor rewards.
- The first heroic ilevel (346) has 22 total intellect plate rewards, 7 of them from vendors, with all slots covered.
- The second round of heroics (353) had a paltry 6 drops, though BoE boots and 3/5 T11 gear available for JP alleviates that.
- The final heroic ilevel (378), has only 4 drops and 1 quest reward. Again, BoE bracers and 3/5 tier 12 for JP cover gaps.
In raiding there are two additional factors:
The first is competition. Suppose that of the healing class/specs, 23% are Paladins (old source). This means that the likeliness of competition is 46% in a 3-heal 10-man. In a 6-heal 25-man, however, that chance climbs to 115%. I wonder, though, if this is more or less than most other class/specs within their armor type. I would wager less.
The second additional factor is armor tokens. This removes the issue of uber-specialized loot from 5 of the 7 armor slots, with waist and bracers remaining. Waist items were available as drops or rep on each level of progression, with a crafted BoE and a Molten Front option as well. Bracers were similarly available as drops and a crafted or vendor BoE.
Now that I am waist and bracers deep in speculation, I will say that I believe Holy Pally raid loot to be successful. There are no glaring gaps, and competition may even be lower than other class/specs contend with.
There is of course the assertions that intellect plate drops more than would be expected due to chance. I have no response to this but "Show me the data."