Calling lotr a children story is a huge mistake, reading it one time is something but the depht of his work is something else. Again, using 2 or 3 exemples to sum up fiction as a whole gender is straight up snobbery, you have works like Isaac Asimov's "Robots" that are actually not just well-written but also premonitory and actually use scientific reasearches of his time to prophesy what's may be happening next and what drifts can happened if things get out of hands. The American and French armies have called on science fiction novelists to imagine scenarios of total war, some of which are now classified as defence secrets and considered particularly realistic. I do not summarize fantasy just by this example, and of course some works are simply published for money and glory, but there are also many uses other than entertainment to a genre that has existed for a long time.
To summarize and conclude by comparing an entire genre of literature to Marvel is a big mistake and even if you don't recognize it, in no way for me is fantasy literature a waste of time, whether it is reading, writing or discussing.
Have a nice evening