Really? "All indications". What would they be?
I see career highs in QB rating, completion %, and YPA in 2016. Those are all ABOVE the levels he reached in 2014. If you take the HC/OC at his word and believe that the first 5 games of 2016 were a growing period for most of the players on the offense, you can see the last 8 games were better still. He played over half a season with a QB rating over 100. That means he was still trending up well after you claim that "all indications" are that he had plateaued. Care to explain that?
Yes, really. You are repeating what I said already. No need for that. I already said he had better rating, completion percentage. Stats are available for everyone.
The opposite argument: In 2014 RT had more yards, more TDs, less interceptions per attempt, more rushing yards. He was a bigger part of the offense and produced more.
So if you extend the 2016 stats to 16 games you would get:
2014: 590 attempts, 66.4%, 4,045 yds, 27 TD, 12 INT, 46 SK
2016: 479 attempts, 67.1%, 3686 yds, 23 TD, 15 INT, 36 SK
It's close, without nitpicking to make a point. He's leveled off imo. Some may say he is better on efficiency, some may say not as good on production, but it's pretty much the same. And in the mean time he had a pull back year in 2015.
Stats speak. I am telling you what I see. Reasonable people can have different interpretations, but I do not see a big difference between the two Ryan Tannehills. To me he is that guy from 2014. He may have a little more succes, maybe a little less success in some years, but roughly that's it.