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

I agree 👍

But I wasn't talking about giving long-range firearms to the Dwarves, but about how such weapons wouldn't become widespread! Because an enchanted, mage-priest-blessed rifle made of cheat-imba-steel would be too overpowered. So, I'm asking: what plot-related obstacles prevented the development of firearms on the surface?

For almost 700 years, the main force on the surface was the new empire built on the remnants of the technology and knowledge of the Shantiir empire. Mages handled long-range combat, and legions of magically enhanced soldiers in imba-steel armor fought in close combat. All development was carried out in magical realms, and no one wanted to mess around with gunpowder.

In the mod, there will be:
1) The remnants of the empire in alliance with desert nomads - the former are more focused on magic, while the latter were too busy fighting and didn't develop.
2) Demons - nihilists.
3) Elves - they sailed away on ships from Tarlad when things got tough; naturally, they are the main experts in bows and wooden magic.
4) Orcs - not interested in progress.
5) Vikings - also too busy fighting at sea; they may know about gunpowder, but they can't technically forge a decent firearm yet.
6) Mages and monsters - they love magic and dislike alchemy because potions are for losers.
7) Necromancers - they can't find corpses with firearms.
8) The Dwarves themselves, who were forced to develop science because of selfish mages.

Added 17 minutes later
The Dwarf race will consist of:

1) Dwarf/Scout/Guard - these are Dwarves on the models of javelin throwers; they can repair golems. Scouts run faster and sabotage equipment.
2) Archers/Arquebusiers/Grenadiers - guys with firearms.
3) Mountain Guards/... - these are Dwarf warriors on the models of mountain defenders; they are armored.
4) Golems/Siege Golems/Fire Golems - you've seen them! These things will break down walls or walk around with a fire shield.
5) Acolytes/Thunder Priests/Pyromancers - mages on the models of rune priests.
6) Stone Giant/Thunder Giant/Lava Giant - giants on the models of thanes; these are Dwarf mages who have received the blessing of the elements - great heroes.
7) Beasts (maybe trained trolls) will be on the model of beasts