"And even if you don't like Cara Dillon's timbre, at least she can sing in tune, whereas Rachel Unthank can't hit the proverbial cow's rear end with the proverbial banjo in the tuning department ...."

What song are you thinking of? Genuine question.

I haven't heard much by the Unthanks - just songs on the radio in passing - but I've never heard anything out of tune.

I also don't recall Rachel Unthank having a particularly breathy voice. I'll go and listen again, but I wonder if some people are throwing the baby out with the bathwater as it were: ie there's nothing wrong with singing softly or gently or conversationally, and that's a very different thing from 'breathy' 'ethereal' Enya type stuff.