Hard to argue that he didn't improve. The biggest sign of improvement are the 4th quarter comebacks and game-winning drives. In 2012, he rarely was able to get the Dolphins in winning positions late in games. This year, I give him credit for pulling out some nice wins late...vs. Atlanta, New England, the game-tying drive vs. Cincy, the late TD drive vs. Pittsburgh.
It doesn't necessarily show up in stats like yardage & TDs & turnovers, but he clearly showed he could lead a team to a win late in the game. That's the sign of a pretty good NFL QB.
He still need to improve, needs to cut down on turnovers, and can't put up terrible performances like he did against Buffalo & the Jets to end the season...when the playoffs are on the line.