The quality that turned voters off Corbyn was a mass front page campaign by the right wing media to portray every little thing he did as evidence of ultimate evil, reinforced by MPs in his own party lining up to undermine him at every opportunity, boosted uncritically by the broadcast media, and endless critical opinion pieces by the "liberal" commentariat. And that was just the first two years. After that they got serious.
I would agree that the media crucified him, but he did on several occasions seem to hand them the timbers and nails and say "Go on, do your worst." I mean, if you don't want be accused of loving terrorists or hating Jews, you don't describe Hamas as your "friends".
This is ultra, ultra basic stuff, that you need to get right before you even think about policies and manifestos, and he often got it wrong.
The quality that turned them off Corbyn was a mild form of democratic socialism, which would have applied to anyone on the left.
That makes no sense at all. Why would people dislike Corbyn for being a social democrat, but like his social-democratic policies?
You've constructed a strawman of an Average Idiot Voter, who thinks "I really want a government that's going to fund schools and the NHS properly by adequately taxing big businesses and the very rich, but I can't vote Labour because Jeremy Corbyn is a mad communist who wants to fund schools and the NHS properly by adequately taxing big businesses and the very rich."
In any case, if you're right, then the British public is simply too right-wing ever to elect a party that's to the left of Labour in 1997, so why whinge about the media?