I think most of us recognise that allowing Cameron to be the main voice of remain was a mistake. He was always a politician of negativity, it's the only way he knows how to campaign, and that's how he framed the remain narrative.Again, you write as if the dominant narrative was of Leave voters making glorious claims as to the economic benefits of Brexit and who are now engaged wilfully in making excuses for that not happening.
The fact is remainers from the get go have consistently predicted economic detriment that would be clearly and obviously down to Brexit.
I think Cameron gave the game away a year or so after the referendum when in an unguarded moment he admitted that the U.K. would be OK.
The longer this goes on it smacks of a political class desperate to stay in the EU and dreaming up the crashing and burning economy story to suit.