Note that LOTR was 100% informed by his experiences in WWI and he sought to impart readers with many of the same feelings. He’s just saying it’s not a 1:1 comparison. For example, World War One had no ents. He just put those in because they’re neat. LOTR isn’t a direct retelling of the great war, but it is supposed to make you think about what war does to people, and perhaps that will make you think about the great war.