HC puts together his grocery/wish list. GM goes shopping. There isn't a HC in the league that does not have a significant hand in putting together a roster.
Since Big Ben left, Steelers have drafted Pickett, Rudolph, Josh Dobbs, as well as signed Trubisky, Fields, and Wilson. I'm pretty sure any casual fan would know this is not what you do when formulating a succession plan for a franchise QB.
The one constant through all of that is Tomlin. He has screwed up the QB spot every second since before the HOF QB he was gifted retired---none of that is for lack of "luck". Tomlin is coasting, comfortable in the knowledge that old man Rooney will never fire him.
That was 14 years ago....3-8 since--including 4 one and dones in a row (about to be 5th).