I can kind of see where you are coming from, but none of that really applies. Take a look at what 3-5 million a year buys you now a days at DE (
http://www.spotrac.com/nfl/contracts/defensive-end/). My opinion on all of those guys is "nope". My central point is that a player with Heyward's combination of age and production costs (typically) north of $10 million per year. End of story. You want that production out of your 3-4 end spot? You have two options pay for it (Heyward) or hope you drafted it and ride the low cost for 3 years or so (Tuitt).
As to the larger cap issues, the Steelers got bit by a perfect storm last time. They paid premium $$$ to Harrison, Woodley, Polamalu, Hampton, Roethlisberger, Ward, Taylor, and Timmons/Farrior all at the same time. That's what happens when you have a LOADED team, miss on a few draft picks, and keep the band together for one last ride (how many out of that group got 3rd contracts?). EVEN w/ all that, it would still have worked if the CBA negotiations hadn't broken down and as a result the cap flattened out for 2-3 years.
So the Steelers had to eat a bit of shit sandwich. Despite that tasty treat, the negative impact was/has been shockingly minimal. Let's count the "losses" to the cap troubles:
1. Keenan Lewis
2. A season or so of Larry Foote
3. A season of James Harrison
4. Say 3 lower end FA's
That's it. I think that Omar Khan deserves a damn medal. He makes ZERO football decisions. Colbert et al come to him and say "Here is the list. All these guys have got to fit under the cap. Make it happen." Year after year he does, and the negative impacts have been fairly minimal.