I've been following this debate and felt compelled to chime in. IMO, Fitzpatrick is far more dangerous a qb to face, without question.
Citing statistics is a misleading way to assess a qb's value; sure, the big ones such as TDs and INTs matter, but completion percentage and yards are not necessarily indicative of a qb's ability to pull out a win.
For years, Tannehill's bread and butter was dumping off the ball to Jarvis Landry and relying on his YAC. When it's third and long and a qb dumps off the ball off for a 5 yard gain, it helps his completion percentage and yards, but doesn't get the team any closer to winning the game ( remember Tyrod or post concussion Trent?).
I haven't followed Tannehill much beyond Bills games, but I think we all know what we saw out there: a QB with no mobility, and no killer instinct to go for the big play when their team needs one. And without that a QB doesn't stand a chance of sustaining a winning record in the league. Fitz, for all of his flaws, does have that instinct to go for it; sometimes it works out, often it doesn't, but at least you gotta chance with him.
As a Bills fan, I will sincerely miss seeing Tannehill on the schedule twice a year