I know that people like to tie things together to present some kind of "narrative" but I don't agree with the OP's suggestion that May's election is the reason for the party standing on the edge of any "abyss" - it was a mixed night for Labour, as it was for all parties - everyone can come away claiming that the glass is half full or half empty for each party
I think that the timings of the results meant that things looked worse for Labour since so much attention was focussed on the one result in Hartlepool and significantly less on the various other announcements.
Hartlepool was a seat that's always going to be hard to defend, given that the previous Labour MP had to stand down due to sexual harassment - which means Labour were always going to be on the back foot - if anything, Corbyn shouldn't have reinstated Hill after his suspension prior to the 2019 election
But the Tories have been throwing lots of money at that corner of the world - look at how the "austerity" agenda has gone out of the window whenever it comes to Ben Houchen - he gets the Freeport and the relocation of Treasury jobs to Darlington and buying an Airport - I'm all for generous bribes but this goes above and beyond the norm (and certainly isn't in line with most Tory rhetoric!)
The rest of the election results were generally better for Labour. They lost some councils (e.g. are now in partnership with the Greens in Sheffield) but picked up a lot of votes in other places - winning things like the Manchester Mayoralty might not be surprising but Khan was streets ahead of Bailey in London (whereas Johnson won in London in 2008 and 2012) - the picture is a lot mixed than the "Hartlepool" headlines suggested - but it's understandable that the media wanted a short sharp reaction rather than picking over the pieces of various local councils over the subsequent days.
I don't even know that Labour are doing that badly in England generally - the majority of the reduction in seats/ votes UK-wide is due to Scottish nationalism - but losing a "traditional Labour" seat like Redcar/ Hartlepool generates more headlines than winning a "traditional Tory" seat like Canterbury/ Kensington
That said, there are a lot of problems ahead. Labour's long term problem has been that people generally don't switch *to* Labour - lots of people start off voting Labour at eighteen/ twentysometing and then move on as they become parents/ get mortgages etc, going from young "rebels" to older "conservatives", but people don't often come back to Labour, they are replaced by new younger Labour voters. The difficulty for Labour has always been trying to retain these voters before they turn blue. You'd think this would be easier for them nowadays as people get mortgages/ become parents older than would have been the case in previous generations. But today's twentysomethings have to be a lot more financially savvy than their parents were at that age - student loans etc - so they are generally more switched on to money
Instead of focussing on the kind of things that twenty first century voters worry about (e.g. zero hours contracts), Labour have been happy to retreat to safe old ground - Corbyn allowed them to regress back to the 1970s - no need to worry about the kind of awkward compromises that Blair needed to deal with to gain power if you have no intention of diluting your moral purity!
Maybe London should give Labour hope though - Johnson won it twice in a row but the Tories haven't come so close since - take Johnson's "sparkle" away from the current Westminster Government and... are voters going to be as excited about Raab/ Hancock etc?
Gordon Brown’s economic mismanagement
How much of the Global recession are you blaming him for though?
Worth bearing in mind that Brown was paying off national debt during the good times and left a growing economy and triple-A credit rating behind (after dealing with the crash)
Cronyism in the Blair/Brown era, showed them to be as bad as the Tories
True, but I think any party would be like that after thirteen years in power - the SNP are going down that route at the moment - look at the latest news about Johnson's House Of Lords nominees
Would have happened with or without Britain
The leftists have been banging on about leadership challenges since the day Starmer was elected.
Thankfully Labour no longer pays any attention to what is an irrelevant, crackpot protest movement.
I think they need to decide whether they want to win over people who aren't Labour members, or just focus on certain "comfort zone" issues (impotently waving their Palestinian flags at the conference whilst ignoring other things) - there's a slippery slope towards blaming the "1%" for everything and getting into conspiracies/ anti-Semitism etc, and I think that some people are relaxed about going down that route