Well, now that Nickelodeon ordered 2-3 seasons of Korra, they have more time to plan things out so not everything gets dumped in the final episode.
Remember, Korra was SUPPOSED to be a 13 episode miniseries. It wasn't till halfway through that Nick noticed it was popular/high ratings and ordered ANOTHER season. Changing their order to 2-3 new seasons at the end of season 1.
Yes, the ending felt rushed, but you can't fully blame the creators for that. If Nickelodeon ordered 2 mini-seasons from the start (which the creators wanted), then it would have been more spread.