I'm not sure about Mordaunt, but Sunak is apparently loathed by many backbenchers.
So was Johnson - until they saw that he could win elections. And Truss definitely is: look how few MPs voted for her. But I can't see Sunak getting the nod after the members rejected him: it has to be Mordaunt for this plan to work.
Mind you, in the last week, I've read of plots to replace Truss with Johnson, Gove, Shapps, Braverman and now, Mordaunt/Sunak. Who next? Larry the Cat?