This is not a myth, but History recording real facts that happened.

Anyone can imagine a "flying car" or a "nuclear fusion reactor". It is a completely different thing having and putting the resources to work: the people, the effort, the money and the time to make something real.

Someone just "having an idea" only works in science fiction, and even there you need to do the work of writing the book, or drawing the comic.

"Execution is everything" is always true after the fact. Good and bad ideas are treated with disdain because that is how people are. Until a random person gets profit from execution, then is praised for the profit, because people desire and envy profit.

If there is a myth here, it is that it matters who executed it first. It's random.

Why is it a myth? Whenever I read about the founding of a big name company there's very often a significant innovation that it's initially premised on.

Disney - animated feature length film with sound, dogged vision of founder

Post / Kelloggs - invention of breakfast cereal, invented by founder (Kellogg's invention stolen by Post)

Carnegie steel - bridge prototype, highly risky and innovative endeavor

Ford - division of labor

Mars - caramel and nougat in chocolate, innovation over Hersheys' plain chocolate, invented by founder

Google - pagerank, invented by founders

Mass production and factories had already been a thing for almost a century when Ford started his factories. It is like saying that the new innovation "computers" was behind Facebooks success.

No, the Ford's innovation is division of labor while producing a complex thing, a car. Instead of a team working on various operations, Ford's system introduced workers who each did a very simple operation, without having to change or readjust. The need for coordination between workers was largely removed, replaced by the conveyor, seriously improving production speed.

Division of labor while producing a complex thing was a concept well established and documented during the industrial revolution before Ford. E.g. Adam Smith had a lot to say exactly about "Instead of a team working on various operations, [...] introduced workers who each did a very simple operation, without having to change or readjust.", it's misleading to call it "Ford's system" because Ford applied it extensively, but he did not invent it and wasn't the first to use it. Conveyor lines also wasn't an invention of Ford - he applied them a lot on scale, but they were widely used in different industries long before he was born. He also wasn't the first to apply continuous assembly lines specifically to the production of cars, as far as I understand the founder of Oldsmobile had been doing high-volume series-production of cars with strong division of labor a couple years earlier, though eventually not as successful as Ford.

He can and should be credited with applying these innovations at scale and ironing out various kinks in the process and popularizing these concepts, but it would be a lie to call it "Ford's innovation", all these things you mention were initially invented by others, although Ford did manage the practical implementation of all these innovations in combination unusually well.

No, that was pioneered by Ransom E. Olds. That doesn't stop Ford from repeating this at every opportunity but it isn't really true.

https://en.wikipedia.org/wiki/Ransom_E._Olds

Which car company was using division of labor before Ford?

Olds-mobile, of course.