I really don't think it is the draft. I'm not sure how well Tomlin stacks up compared to Cowher, but they've drafted a lot of good players under Tomlin.
Brown, Bell, Pouncey, JuJu, Heyward, Conner, Hargrave, Watt, Bryant (for the time he was here and not suspended), Tuitt, Shazier, Williams, Decastro, Gilbert, Sanders...
Of course they've had their misses, but that's the nature of the draft.
The problem is game management and preparation IMO. To me, these losses are so frustrating because the Steelers are the more talented team most of the time. The other frustrating thing is that Tomlin was a DB coach and the only good DB we have was gift wrapped to us by our friends to the West despite spending so many high picks on them.