I think you guys are missing the point. Woldaff already stated that this part is supposed to be a bottleneck. It is NOT supposed to be an easy farm. Having a mob drop the stone every time would make that mob perma camped, and therefore never killed by a lower tiered guild. It would also make the quest a lot easier. You guys asked for trash to have a quicker respawn, and it happened, but at the price of the stone being more rare. When Steel cleared, we had several clears of no stones at all, so having the drop rate decrease makes your two or so clears of no stones pretty reasonable. Really, it was fine how it was, and now I think it is harder, because it wasn't the spawn rate that was bad, but rather the willingness to go farm mobs over and over. Now you have to farm more mobs of the same difficulty and now the lower tiered guilds have to kill the statues (hard trash) even more now because of the change.
You put yourself in a situation where you now have to farm harder to get the result you would have gotten previously from farming less mobs. If you are not taking advantage of the increased spawn rate, then you are just making the quest harder.
Again, this part is supposed to be a huge time sink. Having something drop it 100% of the time would be a horrible idea. Good luck with the farm.