This is correct, and I am aware of this.
Limiting RDM to one element is going to annoy someone (me if the element is not fire, others if the element is not ice or thunder), so I did try to add something by way of options. Magic Burst is a tough one because there's only so many ways to implement this type of mechanic without creating a weird sort of bloat, which is why in the end I decided to turn it into a way to deal AoE damage. Originally it was going to be something like an AoE version of Manablast or Burn/Frost/Shock depending on the enchant consumed. So Magic Burst was originally supposed to look something like this:
I'm not keen on giving RDM AoE bind (since it can cross-class Blizzard II). Same thing with giving RDM an AoE stun (though I admit it'd be handy in emergencies). I also would nerf the potency, since Enfire MB would still be weaker than Fire II in Astral Fire III (100 potency + 87%).58 Magic Burst - Consumes active sword enchantment. Effect is determined by the enchant consumed. Cooldown: 30s. Shares a cooldown with Spellblade.
--Enfire: Deals fire damage with a potency of 150 to nearby enemies.
--Enblizzard: Afflicts nearby enemies with +20% Slow for 20s.
--Enthunder: Deals lightning damage over time with a potency of 30 for 30s.
Spellblade was also going to be designed around unique effects determined by the consumed enchant, but by then I was running out of ideas. >.>;;