Oh me love this kind of questions. I really like geography . Topography is my favorite.
Lets see. Hewitt comes from predominantly desert continent with dry summers and non existent winters. So naturally speaking Aussie have mostly savanna for grass.
On the other side we have continental weather with hot summers and cold winters and well distributed rain patterns. Known for its emerald mountains . (since emerald hills are reserved for Eire and rightfully so, but not exclusively ). So me guess the right answer for it to be Djokovic. Since we have naturally more grass around.
It all depends on what you mean by "natural" really.
Hewitt is much more confortable moving on grass and has a better understanding of the surface's dynamics than Djokovic, who struggles just to stay on his foot at Wimby
However, Djokovic is obviously the superior player overall, and that makes up for his uneasiness on grass.
If they played each other there I don't think Hewitt would stand much of a chance, but I don't know if that makes Djokovic a more "natural" player or not. If I go by my own subjective interpretation of that word, which is a mix of feeling confortable, moving well, having a game that benefits from that specific surface more than from others and being able to use its properties to your advantage then I should conclude that Hewitt is actually the more "natural" grass player.
Doesn't natural mean, "a person regarded as having an innate gift or talent for a particular task or activity."
Hewitt was a great grasscourter.
Let's see here. Let's look at peak Hewitt's strengths on grass.
-Amazing volleys, both stop and drive.
-Great slice to deal with the skidding early 2000's Wimbledon.
-Not a half bad serve. Probably his biggest weakness though.
-Was able to move like Nadal back in the day and had great "sliding" footwork.
-Was able to step up to the baseline and counterpunch all day long.
Certainly watching longer than you, judging by your avatar
Trolls underrate No1e's grass and general game here enormously, while Fed fanatics overrate everyone from and around Federer weak era. Hence all this support for Hewitt, when it is clear to anyone impartial, than No1e is much better and much more accomplished grass player.
Not to mention that their grass H2H is 4-0 for Novak, including the beating baby, almost teen, Nole gave to peak 26 years old Hewitt on Wimbledon.