Yeah it is definitely bittersweet, but if you compare it with the Children of Húrin, it is a very happy book. Boromirs death may be the saddest part of LOTR, but it would be the happiest part of The Children of Húrin, just because that whole book is so dark.
If you have objectively proven that atheists are wrong, that means that you must have proven that God exists right? I do not think that is possible without God showing himself, and not just to you, but to others too. If these atheists have not seen God, you have in fact, not proven that they are objectively wrong.
Also, there are many arguments that atheists use. For example, some atheists believe that the Bible can not be right because parts of it were written long after the events that they describe (for example gospels written maybe 50 years after Jesus’ death, meaning most if not all eyewitnesses have died).
As a Christian myself, I do not believe you can objectively disprove atheism. And to claim not liking God is the only reason for their beliefs is ignorant, if not worse.