Let me put it another way. Looking at my parses, my 51 Monk took 1200 damage from fighting a level 42 guard. My Monk has 1800 HP, so that would have been CH'ed. That means CH is a 3 to 1 mana ratio in this scenario.
With
https://wiki.project1999.com/Tagar%27s_Insects , a 51 Shaman is slowing for around 45% at 125 mana. That reduces the 1200 damage to 660 damage. If you spend 250 mana on Superior Healing, that reduces the total damage take to 136. At level 52 with Regrowth, that 136 is reduced to zero if the fight lasted a minute.
For 395 mana (including 20 mana a minute for Regrowth) the Shaman mitigated the same damage as the CH. CH costs 400 mana.