I'm relieved to learn that my feeling about this is not based on a prejudice against the upper class. Rather, it's just my usual dislike of any singing that tries to sound like someone else.

That's why I can't stand Kathleen Ferrier's folksong recordings. She wasn't from the ruling class and, from the biographical stuff I've read, seems to have been a thoroughly nice person, but her vocal training left her permanently disabled with an RP accent and style of vocal delivery that she could never shake off. Something like "Blow the Wind Southerly" is a freak show.