I'm not sure you'll be able to stop this problem with the harnesses. Often times, hair loss is from the hairs getting into the weave of the webbing and then it being plucked out. For that problem, you'll need a fabric against their skin that would be of a tight enough weave that the hairs can't get into the weave.
Second problem is the friction. The dog is continually in motion rubbing, while the harness is stationary. Back and forth, back and forth. Nylon webbing may not be abrasive when touched, but over time it will have the effect you've noticed. Perhaps a softer lining might work (satin, polar fleece), but over a long distance, it too may have the same result.
Time to reach outside the Basenji family to find rollerbladers that take their dogs with them. They must've come across this problem.
Thats what is great about Ruff Wear they really go above and beyond to prevent the friction wear and the hair being pulled out too