That is a very good premise that is surprisingly rarely used (correctly). The whole "you make the myths people will believe in the future" is a strong trope, and putting the setting in this ancient era lets you do some really weird and unusual stuff. Probably drop an ominous prophecy that the world is gonna turn more bland with time (resetting back to boring old humans and orcs), but just the fact you're all the way back there in time, you can have everything and anything INCLUDING anachronistic technology - because how many time do we hear Atlantis was supposed to have some kind of ancient computers?
I don't want a new campaign world, I want more tools and better reinforcement for my own campaign world.
...because how many time do we hear Atlantis was supposed to have some kind of ancient computers?
Behold, the Antikythera Mechanism
The problem with a young world or "we are first" trope is that there are many fewer adventures. No dungeons, no ruins, no ancient rivalries or enmities. And in politics, how can you have a war over resources when one group can simply go elsewhere and find a new place?

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.