This addition is great, you're right. It's important to remember that the retreat in question is acknowledged to be tactically useful, and that the Denethor of the books, for all his flaws, is wiser and more restrained than the Denethor of the movies.
What makes Faramir's return so horrible is that he has to do it twice. When he first rides back to Minas Tirith, with only a small company, the Nazgul attack, and his own bravery and determination wouldn't be enough to save him if Gandalf didn't show up. We are told, textually, that Faramir is severely fucked up by this episode: he "has been assailed by a great fear or anguish, but has mastered it and now is quiet." That's Tolkien-speak for "screaming internally." He's exhausted, his spirit is spent already, he's holding himself together at a cost. And then he is sent out to halt the enemy's advance over the same field, still harassed by Nazgul, knowing already how bad it's going to be.
Yes, the decision to send Faramir out with the men on a slow retreat is tactically sound, it slows down the Enemy, but not as much as hoped: Sauron had planned out the river crossing, he had a whole bunch of barges ready, his forces were across the very next day, they have "paid dearly for the crossing, but less dearly than we hoped." Which means that his retreat is, in some ways, the opposite of what I associated with it in my original post: instead of abandoning land to save people, Faramir is forced to spend people, not even to gain or keep land, but to lose it slower.
(Also book!Denethor is not a slavering douchebag like he's in the movies, but he still blames Faramir for not taking a ring, still overtly says he wishes Faramir had died in Boromir's place, and still sends him out on a definitely dangerous, potentially suicidal mission with very little love. He's not saying that this is mission is necessary to save Minas Tirith, and that he trusts Faramir's skills as a captain to pull such a horrendously difficult thing off. He's saying that Boromir would have done it better, and implies that if Faramir hesitates to go out, he "lacks the courage to do his lord's will." Rancid parenting. His grief over having had to "spend his son" comes way later, when Faramir's already unconscious and there's no risk of him hearing it.)