It's a little early to bury Nathan. The guy is a proven closer and his pitches have good movement. (yeah, even now) It's his placement that is blowing ***. The fat part of the plate isn't where you want your breaking pitches or fastballs to end up.
I'm okay with giving him some time. Ron makes some split second bonehead decisions, but he doesn't make long term ones. If Nathan continues to screw up, Ron will yank him from the closer spot.
The only time you have to worry about Ron is in the playoffs in a game where the series in on the line. ie, when the Rangers can be eliminated by losing that game. That is when you really have to worry about his decisions making. Other than that, baseball is a long season and everyone makes mistakes. You can recover from those. Ron is a great manager overall. (he has been to the WS the last two years)