Williams has the starting experience and Spence was drafted to be the future starter at the position they just filled via Shazier. There is a lot of support for Spence on this board but obviously the injury is a concern. Spence was undersized with great speed, instincts, and "smarts". If he proves that he can, I wouldn't be the least bit surprised if he wins the starting job outright and never loses it.
If that happens... then what? I would assume Timmons' tenure as as Steeler would be over. He would be a high dollar vet (30 years/old) in 2 years. Back in the day, we always let LBs walk at around that age.