Go back and look at the drafts before Tomlin...the success rate isn't much different.
you have 22 starters on each team, spread out over a career length of maybe 10 years or so. That's about 2 starters per draft (including UDFA), plus some free agents.
I don't think the team has really been that far off the mark lately drafting, outside of probably 2008.
Tomlin's starters/rotational backups (ignoring ST players):
2007: Timmons, Woodley, Gay
2008: Mendenhall, Mundy
2009: Hood, Wallace, Lewis, Johnson
2010: Pouncey, Worilds, Sanders, Dwyer, Brown
2011: Heyward, Gilbert, Allen
2012: Decastro, Adams, Beachum
Cowher's since 2000:
2000: Burress, M. Smith, Haggans
2001: Hampton, Bell,
2002: Simmons, Randle El, Hope, Foote, Haynes, Keisel
2003: Polamalu, Taylor
2004: Roethlisberger, Starks
2005: Miller, McFadden, Essex, Kemoeatu
2006: Holmes, Colon
Draft success to find starters hasn't really changed. A salary cap that went stagnant, combined with recent Super Bowl teams and the allure that comes with hanging on to players who have performed their jobs to the highest level, has left this team in a bad salary cap spot. This has led to players leaving for big dollars elsewhere. Having a franchise QB also plays into that, as they command a much larger chunk of your cap than average QBs do.
Look, one season going 8-8 doesn't mean these current players are garbage, as hard as that seems to be for some people to realize right now.