The instincts to grab balls in the air (e.g., Hemingway, Gallon) don't just happen overnight. Neither does the precision and timing that goes with route running. It's not about drops when you're wide open, it's about battling with CBs, positioning your body, pushing off, and using your hands on defenders to put yourself in position to catch the ball.
We saw with Gardner how rough it can be for a guy who never played WR to try it. I would think Denard would have the same issues, so his role as a WR would be limited for years, if a team used him that way.
Meanwhile, as a runner, his skills are already well developed and proven. He has good instincts for finding wholes and the transition would be pretty smooth.