Tannehill is already Alex Smith's spiritual successor. High floor, low ceiling, get what you get kind of guy. Then again, we all said that with Dalton and he turned it up out of nowhere.
Consistency is so key. When a QB like Stafford, Flacco, Eli or Cutler are "on," they can outduel any future HoFer like Peyton, Brady, Rodgers, Brees. They just aren't "on" 6-8 games a year compared to the truly elite who have 2-4 bad games in a normal season.
I see Bortles being a boom or bust guy more than any of them. He really slings it around. He could be the guy who gets hot and a little lucky at the right time and win a SB over a more consistent, but smaller highs player like Bridgewater.