Really? I suspect there's a wee bit of truth in that, in that a few of the wet, centre leftists might have kept their mouths shut if he'd been doing better and Labour riding high in the polls. But as far as the whole set of Blairites and other ideological opponents of Corbyn they were never going to support him. Ever.
Maybe but my impression (having been a party member for 25ish years) is that most Labour members, even the most New Labour Blairites, would agree with him 80% of the time on core principles (apart from maybe Trident), the only disagreement comes from presentation and how to gain wider support for policies so that they appeal to the person in Swindon, Southampton, Northampton or Thurrock or wherever who doesnt obsess about politics and whose vote Labour will need if its ever to elect enough MPs to form a government.
If Corbyn was reaching out and gaining the interest and support of normal non aligned people as Blair did in 1994-1997 or Cameron to a lesser extent did 2005-2010 the whole PLP and wider Labour Party would be behind him.