RTF is a global modification that replaces all towns in the game.

Even so, dragons can use this to create an entire pool of mercury. And do devils feed on this gray substance? And do angels make necklaces out of gemstones?

Yes, such a huge amount of resources is unjustified, especially for such useless ones. Mercury, in particular, is completely unclear why it's needed for creating dragons. Gemstones and crystals, for example, can be used in construction for decoration, but sulfur and mercury are only used by alchemists and mages.