For most people, this is a bad shot to take. But he is so proficient at making it, it's not really that bad of a shot to take.
It's just like Dirk and his 1-legged fadeaway. For 99% of the league, that would be a dumbass shot to take. For Dirk? It's bread and butter. How about Kareem and his skyhook? Probably not a strong suit of a shot for most people in history, but he rode that shot to being one of the greatest basketball players ever.
Curry generally can consistently hit long threes, or heavily contested jumpers, because he has worked on his shot so much. He was off a bit last night, but then again, all players have those nights, including Dirk with his fadeaway and Kareem with his skyhook. When it's all said and done, we may be looking back at Curry as the greatest jumpshooter to ever play.
Also, you forget to take into account the value of 3s. Say someone shoots 65% on 2pt shots, and another person shot 45% on 3pt shots. That is a 20% difference, which seems huge. But if you shoot 100 of each shot, what is going to get you more points? You will get 130 pts on 2s, and 135 pts on 3s.