John Mackey had the build of a RB in today's NFL, that's the difference. Gronkowski, Graham, Davis, Cameron, Gates etc. are all taller, bigger, and yet just as fast. They're a complete matchup nightmare.
In 2011, 5 of the 15 players in the NFL with the most receptions were TE's. That never happened before in the history of the NFL. In 2012, that figure was 3 TE's, and this year that figure was back down to only 1. However, a large part of the decline has been a result of Gronkowski being constantly injured, Hernandez getting arrested and Tony Gonzalez aging.
Mackey was ahead of the curve in his day, but the evolution of the TE position in the passing game is certainly becoming more prominent in the NFL.
This year there are a very good crop of TE's coming out of college and rest assured that they will be playing an important role in offenses around the league.
I dunno. Reason I brought it up was b/c I don't remember Hackett using a TE much at all at Syracuse. Chandler led our team with receptions but our WR corps blew chunks this season.