You don't see any race cars with airbags do you? That's because a harness makes airbags totally useless.

A Viper bud of mine was wearing his harness at a track when he went head first into a wall. The airbag deployed and he said the 5-point harness kept him from ever even touching it. That would not be the case with standard 3-points. He said he remembers it all in slow motion and actually saw the airbag deploy.