The way I read your comment was you completely disregarding the heal as if the bonus duration was all you got for Mantra. My bad. I agree the bonus root doesn't feel great, but I still like RW more than RQ late game since it forces so many things (RW into Q forces a gap closer of some sort and also halfway refreshes Mantra if it does go through). It doesn't feel great to use, but every ability doesn't have to have an MLG #bigplays feeling to it.
I feel like adding grounding to it (or whatever) will just make RW more obnoxious to play against than it already is since it is now a guaranteed root (you run faster than they do and they can't gapclose) and provides a lot of unnecessary utility (completely destroys some champions with a point and click button such as Riven, Kalista, and crew and also anyone immobile since Grounded also makes it a no-flash-zone.