There's a difference between being Ne/Se and being a creative type. When you're an experimental thinker you don't finish things. I work as a soundtrack composer and don't develop 9 out of 10 projects because there's always something more I'm aiming for and find myself needing breaks from work and thinking, to approach that something better and fresher the next time. It's a true perfectionist's issue of quality over quantity, having the right mindset. (Or, to add, in my case as an Ni primary, already getting the big picture out of it and not wanting to complete a detailed art form.) Compare with Mozart, commonly typed as P but has tons and tons of completed works; he worked every day quite productively. I don't think an understanding of P and J is as fleshed out as one would easily assume with a speculation, especially with introverts where it often has no strict bearing. We just assume creative types are P because they're expressing something new and uncertain to themselves, but it's not the exact case.
However the reason I say Da Vinci as INTP is that he seems more analytical and meticulous than I would expect of an INTJ, rooted in laws and logic more than the idea and its possible application. INTJ and INTP thought simply moves backwards from one another. One reaches out to encompass logic in a selective fashion, while the other bases all their thought and understanding on it.
For further reference/help, a few INTJ characters often mistyped who come to mind are Dr. House, Brian that dog from Family Guy, and Carl Jung himself; those are Ni primaries who exhibit stereotypical creative P behaviors. When you look at all INTJs together, it's not a big difference in mental attitude, just how they're comfortable acting.