Looking at PFR's play index, he had some long completions (one of the lower long completion to total completion ratios, but not at the very bottom), but he still had had the single lowest yards per completion rate of any qualifying QB in the NFL this year.

The bigger problem is that his short passing game was way too short. He averaged 7.8 yards per completion on those plays, worst in the league among qualifiers, while the second lowest (Carson Wentz) had nearly half a yard per completion higher on what PFR lists as "short" passing plays.

It seems like the bigger problem was the lack of an intermediate passing game than the lack of a deep one. But there was definitely a problem either way, one where defenses weren't too bothered by Bradford having a high completion rate.