Let me correct you: The Steelers used to build well through the draft. That hasn't been the case lately. They used to have depth at almost every position. Ben's last contract was fine because he was entering the prime of his career, and there was enough talent to work the cap, and still be able to compete for a championship. This year, they were forced to sign Keisel and Harrison off the street. Worilds was never that good to begin with, but they had to use the transition tag because there is nothing behind him. Taylor and Polamalu are aging veterans with nobody waiting in the wings to replace them. Of course I'd keep a couple good young players under reasonable contracts like Shazier, Tuitt, and McCullers. I'd keep Heyward. I'd be forced to keep Timmons because of his monster contract and dead money implications. He's still serviceable, though. Allen and Thomas? Gone. Jones? Not sure. Keisel, Harrison, Worilds, Polamalu, and Taylor? Gone. 7 starters. Yeah, I'd say there might be some turnover there.
Ben will be 33 next season, and entering the twilight of his great career, not the prime of it. His current contract has nothing to do with the effects of the next one.
You are basing your whole argument on what they've done in the past, under different circumstances. I'm talking about what's best for the future.