The "this defeat was all about Corbyn" take has to explain why we got the very different results we did (in strongly pro-Brexit seats especially) two and a half years ago when we *also had him as leader*.
Now, it is quite likely he became (even) more electorally toxic in the intervening period. But given how differently "leave" areas performed in this election to "remain" ones, I can't help feeling this sort of ignores Occam's Razor. In 2017 we promised to respect the referendum result, this time we did not.
(or at least were overwhelmingly perceived as not doing so by those who voted for Brexit)
This enabled Johnson to run the sort of campaign that May had wanted to, but couldn't, last time.
In every case since 1983, the party leader viewed to be the most capable Prime Minister has ended up as Prime Minister following the election. Only Thatcher in 1979 was seen as less capable than her opponent, however the government itself was very unpopular.
Notably Johnson was seen as less capable than May was in 2017, however Corbyn was down even more since 2017. Johnson may have more popular among Leave voters than May; Ipsos Mori's crosstabs don't show referendum vote for some reason.
The regional breaks were interesting though:
Northern England: Johnson 44% (-5 on 2017 May), Corbyn 33% (-3), Neither 17% (+11)
Midlands + Wales: Johnson 46% (-5), Corbyn 28% (+1), Neither 15% (+4)
Southern England: Johnson 49% (nc), Corbyn 19% (-19), Neither 21% (+17)
Greater London: Corbyn 42% (+1), Johnson 33% (-13), Neither 17% (+13)
Scotland: Corbyn 32% (-22), Johnson 29% (+5), Neither 28% (+17)
There was net movement towards Corbyn over the Conservative leader in the places where Labour lost most of their seats. Obviously these are sub-samples, so have a wide margin of error (the VIs for the regions were in line with the actual outcome), but there's very little fall in Corbyn's rating outside of Southern England and Scotland. Even those who said 'Neither' voted at the same ratio as they did in 2017, a basically 2:1 to Labour.
I'm not 100% sure what to make of the regional variations in most capable PM compared to people's votes, tbh.
Ipsos Mori (Con-Lab):2019 -
Johnson 43%, Corbyn 29%, Neither 19%, DK 6% (+14)
2017 -
May 47%, Corbyn 36%, Neither 7%, DK 8% (+11)
2015 -
Cameron 42%, Miliband 27%, Clegg 6%, DK 25% (+15)
2010 -
Cameron 33%, Brown 29%, Clegg 19%, DK 19% (+4)
2005 -
Blair 40%, Howard 21%, Kennedy 16%, DK 23% (-19)
2001 -
Blair 51%, Hague 14%, Kennedy 14%, DK 21% (-37)
1997 -
Blair 40%, Major 23%, Ashdown 15%, DK 21% (-17)
1992 -
Major 38%, Kinnock 27%, Ashdown 20%, DK 16% (-11)
1987 -
Thatcher 45%, Kinnock 27%, Owen 13%, Steel 8%, DK 7% (-18)
1983 -
Thatcher 46%, Steel 25%, Foot 15%, Jenkins 6%, DK 6% (-31)
1979 - Callaghan 50%,
Thatcher 31%, DK 19% (+19)