I'm going to go against the general grain here and say that it's about half and half.
Suppose your academic score was out of 20. Then 10 marks would be based on your natural talent and 10 marks would be based on your work ethic.
If student A is "naturally smart but rarely studies", he might score a 9/10 in talent but 2/10 in work ethic, giving him 11/20.
If student B is "average intelligence, but works incredibly hard", he might score a 5/10 on talent but a 10/10 in work ethic, giving him a 15/20 (higher than student A).
If student C has a learning disability, his maximum potential is going to be naturally lower than another student's maximum potential and it's going to require more effort from him to reach the same scores as someone who's naturally smart.
Although from an economics perspective, you should consider whatever marks you lost in natural talent as a "sunk cost" and not focus on it too much. Your aim is to maximise your marginal benefit - that is, make the best of the situation you're in. You may not be as naturally smart as someone else, but you can still beat them if you put in more effort. Similarly, you may be naturally smarter than someone else, but score lower because they worked hard and you didn't.
tl;dr - Don't worry about being "naturally smart". It's out of your control. Focus on the things that are in your control and you will find it much easier to succeed academically and in life.