its more than stats, Spearing covers much ground, even if he doesn't get a tackle he dose hurry, close down passing options and chases back very quickly, think about the Spurs game, he would have stuck to Modric like a shadow, and maybe cover with Skirtel.
i'm not saying he should replace Adam full time, just that he is better when we are chasing the ball in some games, and replace Adam after 60 minutes.