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!
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!