Some dogs have thin fur for warm climates. Some dogs have thick fur for cold climates. All dogs shed fur in the summer and grow it in the winter. Coat colors are important to dogs, as far a camouflage and heat trajectory goes. Hairless dogs and cats are from climates that are so warm coats would just get in their way. True, coats could protect them from the sun and exterior heat, but they would also trap heat produced form the animal.
This is a chart that shows the thickness of some Japanese dog’s coat. Hokkaido dogs have a much harder time hunting in southern Japan because their thick coats keep them so hot. Their fur traps the heat that they generate when they run, and it is already much warmer where they are if they hunt in southern Japan. Imagine running through mountains on a hot, summer day wearing winter clothes. (You don’t stop running until you catch up to what you’re hunting.)
Kai, Kishu, and Shikoku have about the same thickness of fur. Some dogs in these breeds may be bred to have thicker coats, different colored coats, thick scruff (Juno’s father was bred to have it) or whatever you breed them to have, but the breed as a whole has about the same thickness as the other two.
Akitas do not have the thickest fur, but they can have the longest. All of these breeds have a long- furred variety, but the Akita is the longest furred. They can also have very thick fur, though nothing to match the Hokkaido. I know someone who has an Akita that has so much fur that you can brush one of his legs, throw out the fur ball, vacuum, and there will still be dust bunnies of fur floating around.