Not a fan of it being Earth. the ether electricity and crystals are a bit too out there. Reads more a Lost Colony type thing. Deposited there, the mother ship had the equipment to make the spires, but the ship moved on. Left them with hydroponics knowledge to grow food, at least some electronics, Journeyman has his instruments to check crystals, and electricity. They have metalworking, but it sounds like iron rusts FAR faster there than on earth, from the talk on gun barrels and sword rust spots. Maybe connected to the ether electricity, but to change the atmosphere so much and people survive? No.
Genetic manipulation of the warriorborn sounds likely. I'm thinking it is a recessive gene, because they spoke of the possibility of the heir to a house being a warriorborn - so if two apparently normal people can have an heir that is warriorborn - recessive. I also note the 4 warriorborn we have seen - Benedict, Esterbrook, Sark, and Ciriaco - are all men. Possibly there are female warriorborn, but just less in number.