They couldve given Gengar a lot of more useful things than freaking Cursed Body if they were just going for consistency. Cursed Body for Levitate is a straight nerf and they know it and they cant talk about consistency when they have dex entries for Vika and Dicidueye praising their speed.
Dunno, maybe Ghastly Strength? AKA Sheer Force clone? Probably a bit too good on Gengar despite Assault Vest being a thing. It's main attacking options benefit from Sheer Force.