That's the NBA record for most 3s scored in a season, by Steph Curry at the 2012/13 regular season. Ariza is averaging more than 4 per game as of today. He has a legit chance of breaking a new record staying healthy. He just likes the three and has ton of easy shots playing next to H&H; pronably he's gonna be surrounding the 40% area. So we'll see.
Ariza is relatively easy to guard because he can't shoot off the dribble. If he continues to be deadly, teams will run him off the line and his 3-point attempts will decline. Very little chance of him breaking the record IMO.
So Harden gets uncontested layups, and they get slaughtered anyway. I imagine most teams would rather protect the paint than the 3? Plus, he just spots up in transition and drains them anyway - you can't really guard those ones effectively.