Do you realize the last first round pick the Broncos have used on an offensive player is on Tim Tebow? Elway has clearly made it his mission to build a great D even if the offense suffered a bit, and he's augmented his draft picks with the free agents you mention. Obviously, it's worked.
He clearly made it his mission 2 years ago when he realized his defense was too soft to win a title. And what does the 1st round picks matter? He used 2nd round picks in recent years on Ball, Latimer, Osweiler, and a 3rd on Hillman. Using the first round pick data is quite misleading. He has spent plenty of valuable resources on the offense - Osweiler and Hillman were good picks. Ball and Latimer clearly weren't but I'm not arguing against his draft record.
He also signed his QB in FA, added a great WR in Sanders in FA, already had a very good TE in Thomas up until this year (he gets credit for recognizing his potential), etc. What position other than OL could he have spent his first round picks on?
Elway deserves credit for recognizing the small window of his team and absolutely nailing it with his FA signings to put them over the top. Peyton, Ware, Sanders, Talib, Ward, etc. were all part of a GFIN strategy that worked like a charm. All of those guys obviously played major roles the past few years.