(And by the same token, if you've only heard folk songs sung by classical concert performers you're probably going to find a version sung by Phil Tanner or Walter Pardon equally strange).

Personally, I find a greater disparity between the old traditional Singers and later Revivalists more evident that that between (say) Phil Tanner and Alfred Deller. I'm not sure who first effected the Revival Folk Voice, but as a genre it's totally affected & even more remote from what the old singers were doing than seems to be the argument here with respect of Pears et al. At least they weren't so contrived as to assume they were being in any way authentic, other than on their own terms of course. Is that the problem here I wonder? Folkies feeling threatened because despite their best efforts the old songs still have a cultural currency that has nothing to do with Folk?