No, the problem is that people are being shot at, pure and simple. That's the only thing that's changed from when the Army and Marines WERE meeting their goals. And it's the main reason why the AF and Navy are still making their numbers--there's a perception, based in fact, that those services are a safer alternative for those interested in military service.
The author makes a few points, but he overanalyzes. What's going on here is a test of the all-volunteer military in time of protracted military engagement. Nobody has ever tried it before, and the jury is still out on whether it will work.
People were being shot at after 9-11, and the Army had no problem meeting its recruitment goals.
What changed? After 9-11 the nation was united. Now we are not.
I think you are right. Not enough people in the Army to give relief to the back to back combat tours.