Good point.
The music I mainly like usually benefit from a characterful non-singer, and would sound worse with a 'good' singer. But yes, when I do jump over for a bit of soul......... I go for good singers.
Yet there is a version of this concept even in the soul world. You have to clear quite a high bar to sing soul, but once over the bar it is the ones who can put the feeling in rather than the best technical performances which are best. Need I cite "I will always Love You" compared to say Uretha?