I don’t know the snswer, and I am a lot more curious than hypercritical. I do know that my dad went to Europe for WWII and stayed til it was over. I have seen admissions that thesae rotations mean discontinuity of effort and presence in the theatre. It is hard for me to understand how 150,000 stretches a force that is 10 times that big. Suppose this were a life or death existential fight for survival. Would we do it this way, or is the rotation a way to make the job more pallatable to volunteers?
Part of the problem is that the military is still a bloated bureaucracy. We have more generals of all ranks now than we did in WWII. Those generals have commands and they have staffs. We have a senior enlisted adviser, as I just learned, for the JCofS. In the 60s we created senior enlisted positions for each service. They have staffs. About ten years ago the SMA sexually harassed a member of his staff - another SGM. If I were King for a day, I’d do a lot of cutting.
That said, it was the administration's decision to rotate units rather than mobilize the country. We could have built a military like we did in WWII. We didn’t.
During Vietnam, once all the units were in place we sent individual replacements. The tour was a year. Lack of cohesion became a factor. I went over with a unit of the 4th ID for my first tour. My second tour was as an individual replacement to be assigned by USARV once in country.
Sure, we could have assigned all of our combat troops to Afghanistan and Iraq back in 02 and 03 and, unless you were killed or wounded, you stayed there. Just typing those last two sentences makes my blood boil. If you or anyone else thinks the Army is stretched too thin right now, I don’t think you could even imagine the repercussions had we done a “for the duration” policy.