It is intriguing really. Blair’s huge vote was because he kept the traditional legacy union vote, when people were still in unions, he got the soft Tory vote and he didn’t have to deal with a vibrant SNP.
Blair fed the SNP by giving devolution. It has ended up costing labour 40 - 50 banker seats over the long term. Michael Foot kept all those seats.
Globalisation, which Blair cheerled, has contributed to destruction of trade unions.
Migration which blairites and employers and globalists supported hugely contributed to the rise of UKIP/Brexit party.
I can see how being pro Palestinian and Irish human rights, sharing platforms with their activists has hurt Corbyn. But really a lot of this mess is Blair’s legacy.