Lot of truth here. They have some good players on D but the closest to elite in recent years was Shazier, now unfortunately no longer active.The Steelers haven't had two dominant players on defense since Casey Hampton & Troy Polamalu retired, that's why they haven't been to a Super Bowl. All 6 Super Bowl wins happened when they had a DT would was doubled or triple teamed which opened things up for the LB's and DB who teams feared and couldn't eliminate.
Though the game continues to evolve and I think they had more than enough offensive talent in recent years to have advanced further. But the talent couldn't be adequately and efficiently leveraged. Lots of sloppy plays, picks, not enough red zone TD conversions etc. Especially, oddly against lesser teams. Blame whoever, OC, QB, HC, but they've had great lines, great skill players and a top echelon QB and a very offense friendly rules structure, but have too many bad losses.