It's a problem when it comes at the expense of the job's versatility. Were the idea more like a RDM samba-esque effect where anyone hitting the same mob they are gets the 15% benefit, rock on, but as a standalone spell, eh... Keep in mind I'm speaking to try and offer incentives to that concept of versatility, not seesaw things one way just because we happen to have "mage" in our job name.
Stop with your terrible aura effect ideas, you and Hyrist have been barking up that tree for 2 years now. What good is a samba effect to a RDM that wants to nuke? Its useless. It is meaningless. You state that people here want to staple RDM to the backline, yet your ideas would staple it to the front line.

A single target spell castable from anywhere on the field of play keeps our versatility in tact. I can cast it while healing, I can cast it while nuking, I can cast it while meleeing. I don't have to stand next to the melee to give an aura, I don't have to strike the mob to give a samba.

You want versatility then you want a spell, otherwise you just staple yourself to the limitations of how that aura/samba effect is applied. Be it standing on the front line nuking (and eating AoE's you shouldn't have to), or meleeing (which screws people who like to nuke/heal.), or married to the WHM's hip giving of an aura buff to them.

Single target spell or gtfo.