What historical myths? The founding fathers or the things they said? Again, I don't know where you are drawing your conclusions from but I think you're a little out in left field somewhere.
First off, do you know what a historical myth is? The term is commonly used in cultural science and history departments, but considering the colloquial usage of "myth", it might look like an oxymoron to the man at the bus stop. After all, "myth" is often used interchangeably with "untruth", "fairy tale", "fanciful fiction" and the like.
In this context, the term implies an identity-building tale, something that helps people to construct a sense of cultural belonging. Historical myths are not necessarily completely fictional, but may just as well revolve around a grossly inflated (and potentially misrepresented) historical event.
In a German context, one such myth would be the Battle of the Teutoburg Forest in 9 C.E., where Germanic rebels annihilated three Roman legions and thus (with regards to long-term consequences) pretty much put an end to the Empire's expansion in that direction. Especially in the 19th century, when nationalism ran rampant, this historical myth was celebrated as the birth of the German nation, a battle for independence, cultural sovereignty and freedom.
In fact, it was nothing of the sort.
The same applies to your Rand quote here. It's mostly intended to instill the reader with a sense of fawning adoration, of nationalist pride, and represents the history of the united states in a way that's supposed to imply that Objectivism was more or less an invention of the founding fathers.
Another example would be her version of the history of the Dollar-sign. I guess she wouldn't have been too happy to learn that it was actually derived from the Mexican PESO. Her theory doesn't even account for the fact that the $-sign was around BEFORE THE UNITED STATES EVEN EXISTED.
With Rand, history always conforms to the way she wants it to be.