I made my setting to be something were heroes and superpowers are new, only starting some two or three years ago and as internally consistent as I can. Because my autism just doesn't gel with magic, gods and aliens having been around since forever and not changing history in all kinds of way.
Quick summary: The Hyborian age and Atlantis and all that ancient humanity stuff happened. But it happened in the fifth planet of our system, which is now an asteroid belt. Two offshoots of humanity survive one hiding in the mistyc dimensions and one flying to another galaxy and becoming the Ancients. To add insult to injury the Power that destroyed first humanity seals a several light years area around the system to bleed off the energy needed for magic, advanced sciences and higher forms of life leaving only enough so natural laws don't break down.
The ancients seeded and manipulated several planets to ensure more than half of all alien species are humanoids. One of the probes even stumbled in the third planet of their forgotten home system. This conicidence allows new humans (us) to subconsciously tap into the Akashic vaults. Mythology and magic, Camelot and Olympus all happened, just not here but to our cousins stranded in other dimensions. More recently the greats of fantasy are just puttting their spin on stories they gleam from them. Sci-fi similarly is based on things that happen to alien humanoids.
Recently the seal around our area of space is degrading allowing us to learn magic, gods to come visit, aliens to come and try to invade, geniuses to invent bullshit mad science and genetic muants to gain reality breaking powers.