There is no extrapolation, Rdm is about as useful as Paladin inside abyssea, that is, not at all.
Depending on the situation a RDM in the group can prove quite useful. If you're low manning then sure, it doesn't make quite so much sense.

Outside abyssea, with the additional refresh other mages have, Rdm still won't be that useful.
I really doubt that actually, and certainly not only because of refresh. Either way, we'll see on the other side of the update.