Rahane couldn't buy a boundary on a much flatter pitch against West Indies last week
It's his first game for India in a while. It was his home ground and his role was to play sheet anchor and release pressure off Kohli. I don't think Rahane can match Dhawan in boundary hitting so that was the only logical explanation.
The question is if it was a good strategy on a belter vs WI. Rahane didn't fail the Indian team. It's the team management that failed by picking him over Dhawan.
As far as his mental strength goes, he's got time in tests and is a very good bat. In LOI's however, I always thought he panicks easy because his SR is not that good.