I think the rot set in a lot earlier. As much as I admire some of the soul work done by Aretha Franklin one of the worst renditions of 'Amazing Grace' was performed by her. No inclination towards tune, timing or beat she just used it, as has been said of others, to show off her voice. Sad realy. If I had a voice as good as that I am not sure if I would want to abuse it in such a way!

Cheers

DtG