Keir Starmer showed you can do it by looking competent and serious.
He doesn't have a charisma to be honest, unlike Blair.
Also, many people voted Labour solely because they voted against Tories, not because people like Starmer and Labour. The fact that Starmer isn't polling well in terms of popularity shows that. But this doesn't matter seeing as Labour won a landslide.
I just hope that Labour and Starmer doesn't end up like the German SDP and Olaf Scholz. The latter won but doing badly as government. Scholz also presented an air of seriousness but is unpopular.