What I've learnt in the past few years is that exciting the electorate and having a positive image - or actively making people think you will lead a better government is more important than being moderate. Now you can't be so radical that you scare many people away - Corbyn
probably did that - but it does seem to me that you can run on a left wing platform and do well, as long as you are charismatic etc. Corbyn was not this, except to a select few people who happen to be active on Twitter or CLPs.
Reminds me of one pundit who was comparing Sanders to Corbyn. She said Bernie Sanders reminds people of an old cantankerous uncle who likes to argue but slips his nieces and grandkids a little cash. Corbyn however reminds people of a cold bookshop owner who keeps eyeing customers and guilting them to buy books.