I've not read the leaks, and I'm not going to (it's like 1000 pages), but I've read most of the Forde report a while back, as this seems to make the most sense to concentrate on, as it covers the leaks.
As for Labour leaks and Forde report( (which covers it), the culture within Labour was clearly terrible and badly organised, but it was on all sides, neither side wanted to listen to the other, and back then they had absolutely zero chance of winning, unless being on relatively the same page. Ultimately the leadership chain is at fault for allowing this to happen or facilitating it, and that buck stops with the guy at the top.
The forde report said the various sides influenced decisions, but it was bad both ways, but sides favoured their side, rather than the election win. From what I remember, neither of the factions wanted to lose the election and didn't work to that on the whole, they were just more prioritising their side. In either case, the report said it had little influence on the actual result of the election.
The right folk didn't want the party going too far left as they never thought it could win, and the left folk wanted to move away from the right (who they couldn't win without), they're both entitled to think what they want, but back then they couldn't win without each other, as then need each other plus some more votes from the Tories. This still applies, and is seemingly going to cause problems with voters again, do a degree.
The report is clearly good work, and its helped move Labour in the right direction and enabled the party to try and work towards the same aim, and Starmer's been much better at removing those who don't want to be a part of that.
But, why did it take a leak for this to all come out, why didn't Corbyn realise this and get a grip on it sooner?
I didn't watch the Al Jazeera documentary, as I don't believe they're reliable/ neutral.