An interesting piece at Catholic Word Report. Küng died a few weeks ago, which I had not heard. I'm one of those who considered him a noxious influence on the Church back thirty years and more ago when he was in the news fairly often. So knowing that he thought so highly of Mozart, and for good reasons, raises him a few notches in my estimation. He shares a love of Mozart's music with Pope Benedict XVI--and Karl Barth.
Personally I agree with someone in the comments on that piece who prefers Bach. To my taste he is more often profound than Mozart, who, after all, only lived until his mid-30s, which makes the comparison somewhat unfair--and his last piece, the Requiem, certainly is in the same transcendental realm as Bach's great works.
But in any case Mozart was a freak. There are geniuses, there are prodigies, and there's Mozart. See this review of a Mozart biography in The New Criterion:
...a four-year-old boy sat down at the harpsichord in his parents’ house and began to play. His sister Nannerl, age nine, had been practicing a scherzo, and he was taken with its lively rhythms. When she finished, he wanted to give it a try. Their father, Leopold, a composer, violinist, and music pedagogue, was astounded by what happened next: the boy immediately caught the gist of the piece. Within half an hour, despite being unable to read music and having had no previous harpsichord instruction, he had learned it by heart.
I mentioned in a recent discussion of Allegri's Misere that one of the ways it was made known outside the Holy Week liturgies of the Vatican was by Mozart attending a performance, then going home and writing out the music. I suppose there are other instances of extreme and extremely precocious talent, but as far as I know none who not only had the innate facility but also had whatever it takes to produce great mature works.