Susan Hall is a bad candidate but she isn’t in my opinion any worse than the previous Tory mayoral candidate Sean Bailey who came within 5% of Sadiq Khan at the last mayoral election.
The problem imo is that whilst the Tories are extremely unpopular in London Sadiq Khan isn’t very popular either. He seems to be less popular in London than the Labour Party is. Which might explain this:
While the polling has a fair lead for Kahn, on the ground canvassers have apparently been getting much less favourable feedback
So whilst the feedback on the doorstep might not be that great i suspect that Londoners will vote for the Labour candidate on May 2, which is presumably what they are telling pollsters.
Labour losing London, however unlikely, would be a massive boost to Rishi Sunak and could well have a profound effect on the next general election result.