Seems to me that you don't understand what happens to prices once certain materials (or in this case the special currency used to purchase them) are being farmed by an increasing number of players. Short answer: They plummet like a lead weight.
The prices you are used to seeing on the Market were due to the relatively small number of players that were in a position to farm the tomestones and spend them on mats rather than gear. Ever since they altered Wanderer's Palace to 'payout' the same number of Philosophy and Mythology stones as Amdapor Keep, it's become much much easier for every level 50 DoW player to farm them. The reason for the 'delay' was due to those new 50s needing time to gear up. Now that their main class is geared in Darklight and they have their Relic, they can farm the stones and buy the mats to sell.
In fact, I'm absolutely positive that even small FCs are starting to farm them in preparation of the FC Housing coming in 2.1. 100 philosophy tomes per run, average run for Wanderer's Palace with DL geared group is about 20 minutes (30 if they feel lazy). That's 300 an hour for just one group. Large FCs will probably have two or three groups in WP at a time. Just three groups, running WP over and over, can be clearing 900 tomes an hour (roughly). In three hours, every single one of the players in those three groups would have 900 tomes each. That's 3600 tomes per group, or 10800 total. That's 86 potash, in just three hours. From just three groups farming WP. Possibly from just one Free Company. I'm sure you can continue to follow the math as more and more FCs do this. And since most large FCs will have a level 50 crafter of each DoH class...
They've flooded the market. Supply is now outstripping Demand. That leads to lower prices. Don't believe me? Hop out to Mor Dhona and take a look at how many players there on your server are in at least partial Darklight. I'd bet it's most of them by far. There's probably /shouts from players seeking to sell their tome mats.
tl;dr The large number of players now at end game combined with a fast-running dungeon to farm has led to a glut of tome-bought crafting materials. THAT is the reason for the price drops. NOT duping.