I think that Cahill and Stults's highest purpose is to eat innings. If they can reduce stress on the bullpen and run clock until bringing the young guys up is a choice rather than a necessity, they'll have done their jobs.
It's an academic point, but I didn't see any reason to believe

that Harang wouldn't be effective and durable again this year, and I doubt I'm alone in that. At the time, I assume the FO simply thought that they could get a reasonable proportion of the performance for less $$$.
I'm not going to be bothered if the team gives Cahill a fairly long leash, just to see if he can bounce back. I think I've got a pretty realistic handle on what this team is, and, despite that,
I've found them pretty entertaining to watch so far.