Without a doubt Dak wasn't as consistent as he could have been, but, again, that doesn't mean he has peaked. The running game wasn't as consistent either, and as fans continuously tell us, the coaching left plenty to be desired/
As for Tannehill, he had a very good partial season, but I wouldn't bank on him being as good as Dak based on that. Dak has a career passer rating of 97. and Tannehill has a career passer rating of 89.8, and Tannehill had a career high QBR, and it was still lower than 3 of Dak's 4 seasons, including this past season. Dak is also 5 years younger.