One of the things that irritates me a little about Da Vinci is he gets disproportionate credit for inventing things that don't actually work. The list of things he invented that he actually got to work is vanishingly small.
Even when claims are made that he is "prescient", there has never been, nor will there ever be a functional "helicopter" that looks like Da Vinci's helicopter.
You always compare people against their contemporaries. Da Vinci has his reputation because he was exploring ideas far above and beyond his contemporaries, and because his breadth of knowledge and skills covered a wide swathe of subjects.
His killing machines seemed to work just fine [1], although some seem to go towards a more interesting counterpoint for when HBO will make the inevitable series Da Vinci: The Machine, staring Leonardo di Caprio [2].
I actually think the tools and environment are more important that the genius.
There are thousands, maybe millions of people with genius-level intellect, all capable of being the next Leonardo or Einstein. Out of them only a small fraction grew up in the right environment, usually wealthy families, but that's still a lot of people. The next, and I think most important requirement are the tool needed to make the discovery, or even just to know that a discovery is to be made.
For example, if you don't have the tools needed to notice that the speed of light isn't infinite, special relativity makes no sense. General relativity requires even more tricky measurement, in fact it didn't came long after people noticed something was wrong with Newtonian mechanics.
Tools are in the general sense. Physical object like a computer or a good telescope, manufacturing techniques and even maths, think of the "shoulders of giants" thing.
So it would be more like giving the graphing calculator the genius it needs rather than going back in time and giving the genius a graphing calculator.
Yes! During his lifetime, he was mainly seen as an artist. He probably earned well but still magnitudes lower than what he would have needed to get something done. Just imagine if there would have been something like venture capitalists.
I guess in terms of the big five, he was super-high in openness but no so high in conscientiousness. In today's world he would fit better because he could run an institute or a company.
Even when claims are made that he is "prescient", there has never been, nor will there ever be a functional "helicopter" that looks like Da Vinci's helicopter.