You're wrong. A theory is supposed to be based on something. Do you think the big bang theory was just something the scientists thought sounded cool? No, of course they had plenty of evidence and research to back it up. Though of course they could not claim it to be fact since they couldn't be...
Hyrule and Lorule are not just the same world in different time periods. The game isn't called A Link Between Eras. Hyrule and Lorule are clearly two different yet similar Worlds.
Besides, if the Triforce in BotW had already been destroyed when the game starts, why isn't the game world covered...