Actually, a case could be made that the biggest difference between Luck's "success" and Tannehill's remaining question marks at season's end was Ireland's decision not to pursue Reggie Wayne (who made it clear he would welcome the chance to come home).
Consider:
Tannehill:
58.3% completion; 3294 yds, 12TDs, 13Ints, 206 yds/game
Luck:
54.1% completion; 4374yds, 23TDs, 18Ints, 273 yds/game
Then subtract (from Luck) or add (to Tannehill)
Reggie Wayne 2012
106 receptions
1355yds
5TDs
84.7yds game
Now I'm not contending that Tannehill was on par with Luck last season nor that Reggie's numbers directly translate on a 1 to 1 executional basis, but generally speaking, if making a natural #3 receiver in Hartline , who was covered by the best defenders, into a 1000 yd receiver wasn't enough to excite you, then consider the difference a true #1 receiver like Reggie Wayne would have/will make in Tannehill's progression of success.