I've read it now. Obviously unsurprising that some are using those stories against it - though I'm still not sure why the oatcake story would have been made up by anyone? As you say it's an unintersting, incredibly incidental anecdote in the book.
I thought Left Out was excellent. A great insight into what it feels like to be inside a political movement like this, and how difficult they must be to run, given conflicting egos, incentives and philosophies between the key figures within such a movement. While LOTO was clearly a dysfunctional and poorly run organisation (Milne appears to deserve a large chunk of the blame here), it feels like it potentially could have worked if it was topped with decisive and clear leadership. To that end, Corbyn's aversion to decision making and conflict was remarkable, and evidence that he clearly wasn't fit to manage any size of organisation, let alone a country. It's a shame the incompetence argument never cut through during his years in power - it seemed obvious by 2016, but the campaign in '17 was enough to keep him going for another two and a half years. Definitely an argument that the PLP (i.e. those who needs to work with and know the potential leader best) should be given more power, not less, even if that's at the cost of the enthusiasm of the membership.
In summary, I guess JC proved himself as a good campaigner, but a horrible leader. Starmer looks likely to be the other way around, and I'd say it's too early to tell if that's going to become too much of an over-correction.