Are e-cigarettes substitutes for or complements to cigarettes? That matters a lot - and the evidence says substitute. E-cigarettes displace cigarettes. Vaping displaces smoking. Hence the harm reduction benefit at both individual and population level.
Yes that sounds accurate to me. Descriptively, we see lower smoking as vaping rates increase. Econometrically, we find that smoking increases when policies make e-cigarettes harder to purchase or use. Both point to the same general conclusion that e-cigarettes displace smoking.