I wouldn't say Tolkien "failed" to convey that, but was rather subtle about it. Personaly I was much more touched by PJ's Boromir as well, but I don't think that is any sort of mark against Tolkiens Boromir. In the context of the book you were meant to feel as much (or as little) sympathy as Tolkien included (as far as I'm concerend).
"We have flown the air like birds and swum the sea like fishes, but have yet to learn the simple act of walking the earth like brothers."
Dr. Martin Luther King Jr.