Competitive with what? even at the high end of 40k, you are (as a minimum) asking this guy to deploy every two years or so, sometimes putting his life on the line in a manner with which no policeman or fireman could ever imagine. That "free" medical and dental costs him (see the Tri Care plan). Also, unmarried E-4s are not elligible for BAQ and seperate rats.
What folks dont realize is that those extra "benefits" (while looking good on paper) dont make up for a lot of things in a soldier's life. The deployments and separations, the risks that go on even in training, and so forth. 40k sounds like a great starting salary and it is...if you are not moving every 18-24 months, dont plan on buying a house, or saving for kids college education, etc.