This really depends one what you end up killing. For example, when they put me against fire and lightening elemental it is going to be a long slow fight, since they resist my two main damage types. However, if something it weak, or even neutral, to fire or lightning I can drop enemies by my second spell.
Edit: The main issue with the mana regen of the THM is that it is passive. CNJ has two abilites that it can watch and use to get mana. The THM has two, but one require you to nuke something and hope you do enough damage to get a return. The other require you two take damage and require 300+ MP just to turn it on. So the THM sits and waits for mana to come back, and when you in passive mode and have no threat the regen is rather good. The problem is I'm standing there... doing nothing to get mana back. I'll still play THM b/c I love the nukes, but I admit standing still in a fight to get mana back is kind disconnecting for a fight.