In my personal experience, it did get a lot harder from 2014 to 2016. My first TN-1, in 2014, was approved very easily with no issue. Had all the standard documentation and there was no ask for additional evidence.

Renewing in 2016 didn't go as well... I was initially denied at the Port of Entry, had to get a lawyer to coordinate an appeal. That took about 30 days, but eventually was granted a 3 year TN. I worked with Peter Roberts who does AMA's here from time to time on the appeal. Actually can't recommend him enough to any Canadian's looking to work in the US!