All of them were a factor (and more) to a greater or lesser extent.
For me, the future of the Labour Party is not answered by whether the next leader or policy platform is social democrat, Blairite, Corbynism, neoliberal, true socialism and the rest of the buzzwords.
You might be enthused in one or some. You might even recoil at the others. I find it all a waste of energy.
A far more fundamental question exists for Labour and it is not answered by how it is organised at the top. One phrase that chimes with me, and is not a slight against Corbyn despite how it might appear, is “Labour has the right family just the wrong leaders”.
The family is the community institutions I referenced in my earlier post in this thread. The leaders are the party itself.
It has, to various extents and for a long time, tried to coordinate progressive politics and advocate a different society for those it thinks it represents. And yet these same people do not feel involved with or represented by it. The link is broken.
It needs complete reinvention as it faces the toughest electoral prospect at the next election. The comfort is, the people that will continue to define the movement very much exist. Labour should enable them.