I don't see where RBs benefit from First Step. The speed at handoff is capped so the animation can run smoothly. At that point you're already moving and FS won't help. I know there's a speed threshold that you have to fall under for FS to kick in, I just don't see a HB slowing down that much, that often, for it to be of big help. And if he is slowing down that much, he's probably getting tackled.