Perversely, I think if people in other northern towns and cities get a sense that only Manchester and London matter – instead of, as now, feeling like only London matters – it will make them angrier, not the opposite. (Source: relatives scattered across said northern towns and cities)
Burnham's big devolution speech should be taking place in a city not called Manchester (Leicester, Wolverhampton, Coventry, you take your pick) and I would have thought it was obvious why.