Tannehill is a good QB I think, but there are so many good QBs in the league today that he's essentially average.
First tier you have the elites: Brady, Manning (although he is no longer that guy), Rodgers, Manziel, Brees, Roethlisberger.
Second tier you have the guys that are on their way to being elite or on the outside looking in for various reasons: Rivers, Palmer, Cam, Luck, Wilson, Eli, Romo.
Then you have the group of guys that are your franchise QBs with various flaws: Matt Ryan, Stafford, Cutler, Flacco, Dalton, Bortles, Carr, etc.
Tannehill is imo towards the tail end of that group