A .75” is heavier for sure. I just got a PVA .68 taperless 18” and it’s 33.4oz.Pretty close to the same weight as a .750 taperless.
PVA doesn’t taper down as quickly as a factory sporter contour or the PBB taperless so a little extra weight there.
A custom length thinner and then flared is going to be the lightest, but more hassle to get manufacturers to make.