Slow your roll on Steelers' Super Bowl contention until roster shows more

That's basically the message from Pro Football Focus, which says the Pittsburgh Steelers have the 12th-ranked roster in the NFL.

Ben Roethlisberger just said the 2015 Steelers offense might be the best supporting cast he's had during an 11-year NFL career. That side of the roster is top 10, easily. Pro Football Focus seems to understand that, but they have concerns about the defense. Here's an excerpt:

A career year for Roethlisberger coincided with [Antonio] Brown's emergence as possibly the league's best wide receiver and [Le'Veon] Bell's development into one of its top all-around running backs. That offensive trio will likely dictate the Steelers' fate in 2015, but their strong offensive line is an important factor as well.

The other side of the ball is where the questions lie; of particular concern is Pittsburgh's lack of a productive edge rush. Perhaps first-round rookie Bud Dupree will provide a jolt, but right now defensive lineman [Cameron] Heyward is the defense's only true impact player.

PFF highlights two defensive players who should be upgraded: Cornerback Cortez Allen and defensive end Stephon Tuitt.

The questions about the Steelers defense are real. A team that ranked 25th in interceptions (11) and 26th in sacks (33) last year just lost Brett Keisel, Troy Polamalu and Ike Taylor, though you could argue it was time for those players to go.

Now, the Steelers must rely on players they never had to before. The secondary is a total retooling. The three first-round picks at linebacker -- Jarvis Jones and Dupree on the outside, Ryan Shazier on the inside -- must produce in a hurry.

Not sure I agree Heyward is the only true impact player on defense. Lawrence Timmons comes to mind. He's not flashy and isn't an elite pass-rusher but is solid against the run or in coverage situations against a tight end or running back.

Not sure I agree on the 12th ranking, either. The Vikings, Bengals and Saints aren't overwhelmingly better top to bottom than the Steelers, who should be somewhere in the nine-to-10 range.