[Mithadan]

Child, I think that Tolkien's world is not more bleak but perhaps requires more will and courage to tread the proper path. Melkor meddled in and marred everything that was done by the other Valar so that no physical aspect of Arda is without taint or as it should have been. Yet Melkor's actions were not wholely without fair results as Tolkien comments in the Silmarillion. If not for Melkor's excesses there may not have been clouds, rain, snow, or mountains. Perhaps all rivers would have run straight course, all lakes may have been perfect circles and the oceans flat and featureless. He unintentionally created much of the "wilder" beauty of Arda.

Also, the Children, Men and Elves, were at least born free of taint though Melkor's actions inevitably mar their thoughts and deeds. I think that a sub-theme of Tolkien's Legendarium is that the Valar attempted to construct a paradise in the West but were using materials marred by Melkor so that their paradise itself was marred. Despite their best efforts, they could not maintain it free of Melkor's evil and so it necessarily had to be removed from Arda.