I can't really take this article seriously as a comment on literature because it uses ugly language like "attitudinal" and "outright funny". Articles in The Guardian usually reflect a particular part of English society that is highly privileged, politically centrist and conformist, and not as smart as it thinks it is. Those attributes probably also characterize the UK audience for literary fiction. It's annoying and smug, and I guess maybe saying that is ugly itself.
Surely we should sometimes try to diagnose in good faith where thinking goes wrong. Most people have encountered toxic personalities who they have needed to exclude from their life, for example. You might claim that toxicity is always relational, that it takes two. But there is such a thing as pathology when it comes to personality and mental health. To call something toxic is to call out a pathology for having a seriously negative impact on other people, whether those other people are themselves healthy or not.