While I agree Riley is not a finished product, max exit velocities are a lot like FA velocity and typically decline immediately.
Riley will almost certainly improve his plate discipline numbers, and by extension is K and BB numbers. I wouldn't bet on him improving his exit velocities much, if at all.
I could definitely see Riley streak his way to a 3 win season that's better than anything Lamb has done (his first 50 PAs may have positioned him to beat 2.5 wins this year), but that doesn't make him appreciably better.