Can’t remember the exact details, because I’ve been testing other stuff, but I think overall it results in more DPS and since there’s plenty of chaos resistance reduction that it’s not actually a dps loss to use the transmuter. Plus it’s less than 25% due to the helmet adding 16% weapon damage + the flat vitality damage the sceptre adds. So I’d say only 20% or less is chaos damage.
There’s also the fire DoT that can’t be converted without the sceptre, which combines to provide a hefty amount of vitality DoT :3
And so the transmuter is worth using. Sure, it’s not pure, but it works better from testing than not having it.