Nick has mishandled this series since it's inception pretty much. A lot of the reasons for the problems that S1 had were due to that. Remember it was supposed to be first a movie, then a 12 episode mini, then a full season. The extension left the crew with a hell of a rush for Book 2, and it shows. Mir couldn't do all the animation, the scripts were generally poorer, and the scheduling for the show after Book 1 was atrocious.
The ending to Book 1 was what it was because when it was animated, it was supposed to be the end of the series, there were no plans at the time to continue Korra when it was written. The beginning of Book 2 has the issues it does as a result of that too, and the reason that they went with the HUGE big bad then, was again, the series was supposed to end with 26 episodes. Then it got extended again.
I know people have said they wished that the series had more time with Amon, or more time with the Vaatu story, but that was never in the cards. Even if they say, found out that they were getting a second season (books 3 and 4) during production of Book 2, which is what happened,
the process of animation doesn't let you change much once you are in that phase, VO has been recorded, every scene has been storyboarded out, and the die are cast.
Look at the difference in quality of Book 3, which hasn't been rushed, and had the creators knowing exactly how much time they had to work with.
Nick simply doesn't care about the series though, and it definitely shows.