Right, but if you're a GM for 5 years, assuming you have 7 picks per draft, you're drafting 35 players. If you consistently go against the odds, they catch you. Miami has literally been up against the odds for years based on the players and coaches they've drafted and hired. If I'm a GM and I'm looking at a guy who has a strong chance to fail - whether it be due to athletic testing, mediocre performance in college, or some other factor - I want to have a good reason for taking that gamble. You want some elite characteristics that make you believe this player will defy the trends. Players with Tannehill's college career and pro career to date more often than not fail to become franchise QB's. You can point to reasons that it's been harder for Tannehill, but a lot of QB's who had similar career paths and failed to meet expectations also had reasons.
QB is the hardest position to draft. For every limited experience QB (Tannehill) there are several that are taken that haven't played in a pro style offense (RGIII, Newton, Kaepernick). I've seen most of those QBs fail in the pros. There just aren't many QBs that come out without flaws. You have to be lucky to be sitting at the top of the draft, with a need at QB, in the right year. Indy? Twice.
For all the knocks on Tannehill's limited playing time in college (thanks to the idiot Sherman), there is one thing that is ignored, he can throw the damn football. Anyone who claims he didn't have the talent to start all 4 years in college is full of crap. He doesn't show any of the lack of fundamentals that you would expect from an athlete that was moved to QB.