Calculus isn't an invention, it's a discovery. It's not patentable. Calling them the "finest minds" seems a bit of hyperbole, they made great discoveries, but you don't need the finest minds to do what they did (Newton looks rather all too human and of his age, particularly with regards to his Biblical literalism and alchemy). It seems likely that equally great minds concurrent with Newton and Leibniz would have made the discoveries. They weren't in isolation and the progress in maths makes certain discoveries more likely at certain periods when the necessary pieces are in place.