Tentacruel wouldn't be an amazing Volcarona check if it doesn't carry Toxic, Haze or have Liquid Ooze. Uninvested Scald does laughable damage after a few Quiver Dances. Liquid Ooze, Hail damage and a much less effective Morning Sun in Hail does help combat it, but Volcarona can still do a good bit of damage and heal with Giga Drain in the mean time. Besides, using Tentacruel makes us use up our WC slot.
It's still an option, just not as good as it'd seem initially imo.