It doesnt seem the issue is centrist v leftist. Im much more inclined to the latter.
The fundamental issue is that the corbynistas haven't reflected on the reason we lost and this mainly seems to stem from the fact that don't care for the premise that the Labour Party is meant to be presenting an alternative government. Rather we have deluded non-sense that doubles down on a 'socialist movement' that will gain power in some distant future once all the plebs throw off the shackles of their false consciousness. Nothing about the very real role that an Opposition party in the Westminster system is meant to fulfil. This is what most anger me and why I would like red banner types to go to another party with an appropriate modus operandi.
I might add, based on the last electoral results, the plebs seem to be drifting in the wrong direction and the 'socialist movement' line does nothing to reverse this. Quite frankly it is childish and disingenuous. I mean, even John McDonnell realised you need part of the establishment. He spent a considerable amount of the last few years trying to get the city onside (you need money at some point). Example one: https://www.independent.co.uk/news/business/news/john-mcdonnell-city-london-bankers-labour-policy-making-a8312246.html. How does this square with the purity of the socialist movement? Centrism may not be the long term solution, but reaching out beyond your core voters most certainly is.