I've tried coming up with myths for my campaign but I could never solve what I call the Apollo Problem: Is the sun the flaming wheel of Apollo's chariot, or is it the flaming eye of Horus, or is it a giant ball of gas floating millions of miles away? Only one of those things can be true, and it's possible for the PCs (through things like divination, crystal balls, or just flying real high to take a look) to figure out which of those tings is the actual truth.
...
This is your problem right here.
The PC's should not have the power to "figure it out".
Nerf magic.
Problem solved.
Greetings!
NERF MAGIC. Yes, this is indeed what the DM needs to do in their campaign. If the DM is wearing the Viking Hat properly, it is the DM that must first realize that the DM CONTROLS THE CAMPAIGN--the campaign doesn't control the DM. Or more specifically, every aspect of every rule and game system contained within the game--and Magic is one of the campaign's game systems.
Certainly, if the DM so chooses to run a totally "GONZO" campaign--allowing the whole magic system to be used unshackled is most certain to produce a very "GONZO" style of campaign milieu. Nothing wrong with that, by the way--if it is your full intention. However, if the DM has in mind to run and develop a certain kind of campaign that isn't "GONZO", then the DM must review the magic system very carefully, and adjudicate with a swift and ruthless hand. Otherwise, level by level, the player characters will embrace the full scope of the magical powers and spells of the game, and any carefully crafted campaign that isn't "GONZO" will be totally trashed in short order.
Thus, we have here examples within the game of numerous knowledge-gathering spells that do serious damage to a whole landscape of culture, history, mythology, religion, and even cosmology. So, yes, those spells must be brutally stripped from the game, so that player characters actually remain mythical, heroic type characters from legends and history alike--instead of demi-godlike superheroes with a vast toolbox of godlike powers at their fingertips, at a moments notice. Such terrible elements create a omniscient, all-pervasive knowledge base of absolute knowledge and certainty.
That dynamic right there is sure to bury any kind of mythical "wonder" in your campaigns.
In my own campaigns, I use much of the magic system, but I heavily adjudicate it. Resurrection spells, raise dead spells, knowledge spells, gate spells, planar travel spells, talking with gods and goddesses like you have them on speed-dial in your cell phone--no. Fuck all that. All that kind of stuff is fucking gone entirely, or otherwise heavily modified. Any of that kind of thing remains very firmly and absolutely within MY hands--not the players. At various times and places, with certain special events, occasions, or magical items, the players may gain temporary access to some kind of power, though such is very limited, and kept tailored to the restraints of good mythical, historical, and narrative standards--which also combine to contribute to how actual *game play* develops as well, not just in the immediate scenario the players find themselves in, but for the entire campaign.
DM's simply always need to keep these considerations in mind, and put serious thought into them before even beginning a campaign.
Semper Fidelis,
SHARK