Ardor does seem like it should be a RDM spell though, but as a big finisher like Verholy/Flare.
Perhaps as an alternative to those (or even replaces them) when your mana are equal. (Seems odd to me that you're encouraged to keep them equal until you get Verholy/Flare, then you need to make sure theyre not)
Same potency, but gives a bonus increase to both mana and procs Impact instead of Verfire/stone-Ready.