I'm not sure whether wax has increased the lifespan of my chains. I seem to get plenty of use from chains regardless of lube methods. My hybrid/casual bike that I've used a lot on the local groomed gravel/chat trails got more than 2 years and 5,000 miles of use before I replaced it a few months ago. And the chain was still running fine, no problems with the cassette or chainrings. It was a little stretched but I probably could have used it another year. I just needed a narrower chain when I switched the drivetrain from 7-speed to 8-speed cassettes. The original chain seemed to clatter a bit and was more finicky with the 8-speed setup.
I got similar use from the first waxed chain setup on one road bike, begun in summer 2017. That chain is temporarily benched because it was cut for a 13-25 freewheel and short cage RD. When I switched to a 13-28 freewheel I needed a longer chain. So I stored the chain and freewheel together in case I go back to that setup.