The first, as you were writing about, was the jarring back and forth of the story line. I know that it can be an effective technique, but it gave the movie a herky jerky movement, when more of the story could have been told. Eastwood could have portrayed all the battle scenes first, and continued on after with the bond drives and then flashed back. To me, it would have told the story just as well.
The other thing was the overemphasis on "We weren't heroes, the guys who died on Iwo Jima were the heroes." I don't disagree with that, but I am also viewing from the perspective of the present. And to me, anyone who was on that island during the fighting was a hero. No one was safe. It mattered little if one was a corpsman, a runner, or had other duties not directly related to actual combat, everyone was in jeopardy.
Now by no means am I attempting to devalue the actions of those who were in continual combat either. The accounts I have read leave one dazed. I just think Eastwood carried the "We weren't heroes" too far.
Good points. A guy who is on a supply ship is just as valuable as someone actually shooting. No, at that moment, perhaps he isn't in as much danger---but there are other dangers, including the constant threat of subs and air attacks, for which he is almost entirely unarmed and unprotected. Some people are heroes "for real" (Sgt. York) and some people are heroes symbolically, who happen NOT to get shot storming a hill. They went up, all the same.