The only starter I'd have had no issues using on short rest is Dickey. Seems.he could handle it. I found myself actually wishing he hadn't just pitched cause I'd have even used him on 2 days rest.
The other issue is the chain effect. You cannot use Sanchez or Estrada on short rest right now. By using Happ last night you're accepting that Hutch has to come up for a start too. It's a domino effect.
I wonder in fact of they're actually worried that Estrada might not be able to make his next start. If that's the case tthey might need Hutch for that start, making it all the riskier to use Happ last night.