Ok BUT, if you're the GM working with Rex to put together the right roster for the kind of team he's building, shouldn't it ultimately be your responsibility either to (i) force him to adapt his system to the available personnel (to the extent that is possible, which under the Pegulas' "dotted horizontal line" structure it might not have been), and/or (ii) at the very least, if the safety position is critical to the system your coach runs, come into the season with enough depth at that position so that your entire season doesn't hinge on the health of a guy who is one hit away from a wheelchair? What the HELL was Whaley doing all offseason? Does he even talk to his coaches? There were a number of quality safeties available to sign or trade for.
I accept your premise, but to me, it puts equal (if not more) blame on Whaley.