Charm with no cool down would be broken. Also archers have charming arrows to do charm back to back if that's your thing.. charm has no limitations other than enemies that can't be charmed

Immolation is situational. It heals fire based enemies and can't burn enemies immune to burning. In fact, it powers up enemies that benefit from burning. You can't really use it in melee range without hurting yourself (e.g. Even though you are a Mage, melee enemies get into melee range to hurt you,)

That's just 2 examples of how asymmetric a comparison between the two skills are