Perhaps it makes sense, temporarily, to operate and support a small number of airplanes of a new type. But considering the crew training, parts, maintenance etc. - a huge overhead for such a small number. And for a single C-17, regardless of its known capabilities - hardly makes sense.
I don't know the actual numbers, but having fewer than 8 airplanes of a type seems like an unnecessarily expensive route for airlift. And it can't be hard to sell them later, they would be in demand for a long time, I would think.
In the interim, though perhaps it would make sense to participate in NATO's strategic airlift consortium.