He may well be a very efficient mayor, and I think I'd prefer his approach to certain questions better than Starmer's. Would his be a safer pair of hands (for want of any other qualities)? If so, they'd be a very beige pair of hands. I know that charisma isn't everything, but neither S nor B really stiffen the sinews and summon up the blood.
I think though he's been emboldened by polling that suggests that a Labour party with him as leader could win against Reform. It feels very early for him to have done this though. I think he may be the Heseltine of our time.