Well, different people are better suited for different tunes? I've heard the song, and I think I can give a performance. But from my experience, it really is that some songs are just better suited for some performances. That doesn't necessarily mean that someone who sang something else good is well suited to sing another song. i.e., David Lee Roth was a great singer! But I don't hear him doing Country?
So it's really "just the right fit." That the producer is looking for. There could be several good performances but they may not be what the producer hears in his head when he pictures the finished product. I had a friend from Helsinki? EVERYTHING he did was a Finnish product...
There are several here who are not who you would consider singers in their own right, however, on some pieces, you couldn't imagine anyone else doing the performance? Their style "just fits the piece." I wish I could find "a piece..." that fits? WAIT! are we talking about the same thing?