I agree, but I'm not saying that he was unaware or mostly unaware...I'm just saying that his lack of personal experience with the pivotal role of flight (compared to his real experience in ground campaigns in WWI) combined with the relative rarity of flight in the LOTR, might have made it an avenue too exotic in his mindset to be even worth exploring in his fictional universe, even as just a throwaway idea (such as the suggestion of, "Lets just give it to Tom Bombadil"). Flight was often used as an element of escape or last minute intervention, not as a major plot device.