You seem to be making up a narrative to fit their own predetermined view. Quite wide of the mark in my opinion.
You'll find the Iraq war and Tony Blair had a much bigger impact on public opinion of Labour according to polls.
OK, each to his own opinion.
I believe the 'rot' started with many 'red wall' Labour voters (
not those down south or in the suburbs) with Brown's unguarded remark; it 'set in' when it was followed by the loony left being allowed to run the show and then its 'no-where' stance on Brexit. All this caused a hither to unknown phenomenon to occur in 'base camp' Labour strongholds; people not only thought about voting Tory, they did vote Tory, or for other parties, either way enough to give Labour its heaviest defeat in a GE for years.
This wasn't a one off reaction to the Iraq war, which might have happened elsewhere, but not in 'red wall' areas, it was a
shifting of the soul in many Labour areas and until its foundations are truly examined, then Labour will remain in opposition, even when Boris and his ilk are running the country.
People of real working class persuasion/vision in the Labour party have either died off, left for pastures new, or got slung out/side-lined! So called
Public Opinion is always fickle, even what Labour party members themselves believe, is not relevant to gaining power; what is relevant to gaining power is what counts to individuals attitudes and aspirations, and what happens in the privacy of the ballot box with people who hitherto always
voted Labour, no matter what, who were born and bred to it.
This is what has changed, not public opinion/poll numbers!