Sistine Chapel? David? Last Supper?
Michealangelo went about 5 years over and kept his vision of the chapel a closely guarded secret, even going so far as to ban priests from the building for over a year. Look it up..
For David he was not directed HOW to depict him. Simply to create a statue of David. Much like telling an artist you want a picture of a male warrior. He had the absolute broadest possible image to work from, a man, possibly white, possibly jewish, possibly arabic, but definitely a man, who was a warrior, when he wasnt a politician or prophet, depicted in some way that would make him inspirational as an artwork. Rather a far cry from "sculpt me a gay, black, kimono wearing, obvious homosexual".
For the last supper it was "paint the last supper of jesus and his 12 disciples at the moment he revealed one of them would betray him" Which is still extremely broad.
The dress, posture, actions, and emotions conveyed by each of those individuals at that moment was entirely up to him. Even so far as to include Mary Magdollen in a position of extreme importance at jesus right hand (some would say pregnant) at a time when the extremely anti-women catholic church would never have approved of it.
Given what was happening in the world at that time DaVinci likely risked a tormentous as a heretic for the way he drew her into that painting.
But your right, he had no artistic freedom at all.
** when you dont know anything about art you probably shouldnt try to "zing" people on it.