There are plenty of issues with this.
Starting with the fact they ditched Blue Origin as their engine partner in favour of some SSME's that AJR say they will cobble together from the left over parts they've got lying around the workshop.
Were Blue too expensive or where they just bid candy to impress DARPA?
Then there's the fact the whole budget is $146m. I'm not sure if that's going to include the upper stage, which being expendable you want as cheap as possible. OTOH being solid makes it quite expensive (H&S nappies everywhere).
"Attitude" is a difficult thing to assess but you've got to wonder if Boeing has the right attitude to pull this off or are they playing the same route LM did with their X33/Venturestar BS?
Incidentally "Operationally Responsive Space" ("launch on demand" perhaps give you a better sense of what they want) is a thing for the DoD. Partly it's about how fast could they replace a satellite if it was (for any reason) taken out of service.
It's also about how fast could they add capacity (EG comms, imaging, ELINT) over a particular area (say for example the D decides to invade Poland for some reason, who knows) if needed.
Yes this also needs a set of either standardized payloads or payloads you can plug together to perform missions at short notice.