Maybe she didn't have to put that much weight, I think we can also consider the critics as one 'world' (in the article sense of the term). They influence each other, and if a small number of critics happen to find a novel above the average quality I can see how it could spread through their community, just like a viral novel spreads through the general public. Even more so as there are probably some links between the editors/agents and the critics, which could help bootstrap the critic-local fame (and then even a slight push by Rowling's agent/publisher can be enough to play the role of what would need to be 'luck' for regular unknown authors). What I mean is that success among the public and the critics share the same luck/quality mechanism, but independently. Of course there is some influence from the critics towards the general public (and vice versa, although less I guess) but not enough, hence the critically praised novels that still fail to sell widely.