I would be careful looking at things as simply a mana cost/ casting time comparison. The Heal and Nourish comparison does not extend much farther than the mana cost and casting time, as Nourish is better when there are HoTs already on the target but it also refreshes Lifebloom (talented). Letting the lifebloom bloom is a very large heal, so if you wanted the bloom heal and needed to through in an additional heal using Nourish would be a bad choice.
"Just because it's not nice doesn't mean it's not miraculous." - T. P.