ditto to what lisa said, its mostly genetic in nature first, diet related second.
all our dogs eat the same food, Garnet and Juggs shed like sled dogs or labs(and dear lord, when garnet is in heat, her crate is layered in dog hair), the others drop almost no hair, even when brushing.
as far as the "overbathing" goes, i've not noticed a difference. our dogs get bathed when we feel like it, be it 3 times a week, or once a year. Many dogs in conformation shows are bathed a couple of times a week, and there are no coat/skin issues. Most of that is because the dogs had a CORRECT coat for their breed to begin with. Using a high quality, non-lanolin based dog shampoo and rinsing well(and then rinsing well again) is all you need. See what you can purchase from your local groomers, NOT your local pet store. It will last longer, as it dilutes, and its generally better stuff.
for brushes, get a rubber curry comb. if you have a farmer supply store, the kind used for horses works great, and is usually cheaper than the same product in the pretty package marketed for dogs. Brush before a bath, use it to rub the shampoo in, and brush after the bath too.
personally, i agree that you cannot improve upon the genetics of your dog, but you can help them reach their full genetic potential, and sometimes, a high quality fish oil supplement will do the trick. I like Grizzly brand Salmon oil myself, i have tried other brands with the dogs that i either had to use way too much of for it to be cost effective, or it had so many other additives in it, i wasn't comfortable with it.
That, a high fat diet in general(fat is IMPORTANT for dogs, many many bully breeds are put on low fat foods thinking it will help with the overweight issue, which is calorie and carb related. dogs NEED high fat diets), which you can get by choosing the right kibble, or adding things like the fish oil, coconut oil or even olive oil.