Rift is awesome and it seems overall more balance I'm being killed by a lot of different guns not just thorn and last word. I haven't noticed any one gun that is taking over.
As always they'll find a gun that is going to be "the best" or another one to complain about my guess will be hard light from the posts I've been seeing. But even still I think with the weapon balancing the way it is you won't be forced to use a certain gun to compete.