At the same time, I think your son would have been successful regardless of how much time he spent doing his homework. And I don't think he's going to be able to keep all of that up through high school, either.
I'm an engineer by profession, and I work in a senior management role in an engineering firm. When I make hiring decisions, I am far more impressed by a prospective employee who worked an after-school job for 3-4 hours per day at the age of 16 than one who did 3-4 hours of homework every night.
What you said is right over target.