I think I'd still find a way to lose in 45. The crux of it for me is that Starmers personality doesn't matter at all in the current circumstance, much like Attlee's didn't matter in 45, whether silly accusations from the opposition stick or not. Starmers entire opposition tactic has largely been of a laissez faire nature and allowing the gross incompetance and corruption of the tories speak for itself.
He has made a couple of speeches I liked, that showed more sincerity and content than anything the tory front bench is capable.
The PoS johnson for whatever reason could enagage with a section of the public, but his obvious incompetance has led British politics away from personalities for the time being.
In short I pretty much agree with your assessment of Starmer's personality not being an issue this time around, like it wasn't for Attlee. Whatever else he was, churchill was far wittier than any of the current tories and his silly remarks didn't manage to have any impact