The S.H.I.E.L.D. characters don’t have the greatest history of trusting people who come in from the outside right off the bat.
That said, he’s been down in the figurative trenches with these people, forming close bonds and even falling in love.
Risking their lives won’t come easily.
Mack has an advantage of rising to the new challenge of leading S.H.I.E.L.D. thanks to his years of working alongside the agents who will now work under him, so he won’t necessarily face the pushback an outside director likely would have.