The only benefit chill wizards get(for damage) on bosses is that if chill does not apply and you're specced into thaumaturgy and grab the 20% bonus damage(with ice spells) on targets without Chill on the boss. That being said you still lose 7% damage. For those going Oppressor for even more cc then your damage will be…
I would very much like to be able to Chill bosses simply for the damage bonus i get. atm i am losing 6*3= 18% + 9%= 27% damage on bosses because they cannot be chilled at all.