How tough did the DoD think was?
Within scope of similar sized crewed vehicles (IE doable now but this would be a safer option and *might* give a bit more payload)?
DARPA tough. IE Order of magnitude improvement needed.
12000 ft is quite high so any one doing this should be thinking about a much bigger set of rotor blades. IIRC the environment is also pretty warm, knocking down engine performance further.
As a performance spec 5000Lb across 75 miles does not *seem* excessive, but the hit from altitude and temperature may be bigger than it looks. Designing that into an airframe from scratch on a short time frame is looking pretty tough. The Boeing effort does not look like it's in the running.