how is it a gold sink O.O? what it did was increase the prices of Resonance stones.
Ultimate explosion costs the amount of a MFI3 that is way over price.
Since price of oclays is fixed, the gold price of oclay items will be roughly 26g / chance of obtaining it. It will rarely be affected by the overall level of gold in the system.
However, this also means that for every stone created, that much gold have been removed from the system (as the clay gold was paid to an NPC, not another player). Therefore, gold is being removed from the economy at a much higher rate than before (assuming demand of explosions are still the same). Hence, this is a better "gold sink". That does not imply in any shape of form that you'd be able to get stones for cheaper, but you can probably get other items not tied to oclay for cheaper.
I fail to see how an 8% stone costing the same as an MFI3 is "way over price". an MFI3 guarantees one fortification between 1 and 13, which, at max, means you'll gain 2% more attack power (if your entire attack power comes from the weapon, which is impossible), and that's actually roughly equivalent to how much dps increase an 8% stone grants. (in fact, if you're playing assassin, you'd be lucky to get an 1% increase in DPS with an MFI3, as it'd only fort one of your two swords).