You're quoting from the wrong professor and missing the point.
Dr Lade Smith CBE, President of the Royal College of Psychiatrists, said:
“People can experience mental ill-health for a variety of reasons and a professional assessment can often help distinguish between everyday distress and a mental illness that requires medical care and treatment.
“Historically, many people with mental illness have felt that they could not reach out for support. It is a good thing that this is changing but research shows many mental illnesses, particularly severe mental illnesses are still under-recognised and underdiagnosed. The sooner people access care and treatment, the less likely they are to develop a more complex and life-long illness which impacts their ability to lead productive and fulfilling lives.
“It is important that people have access to an evidence-based comprehensive assessment from a trained psychiatrist or qualified mental health professional that will clarify whether or not they have an illness diagnosis but also provide a package of care and support to enable that person to recover and have the best quality of life they can. Many people will be able to engage in some form of work if appropriately supported, but it must be acknowledged that for some people, the severity of their illness will mean that they may never be able to work.
“The significant rise in the number of people being diagnosed with a mental illness in recent years has been driven by real issues that affect us all, such as increases in poverty, housing and food insecurity, as well as loneliness and isolation. This crisis is having a substantial impact on people’s lives, the health service and the economy.
“The Royal College of Psychiatrists wants to work with the Government to ensure that where a person's mental health would, on balance, benefit from the structure, financial independence and social interaction that work can bring, they can access effective employment support and mental health treatment.
“However, for people with more complex, severe and enduring mental illnesses, reducing, restricting or creating further barriers to their access to benefits will only make them more ill, and in need of more NHS care.
“Mental health services must be provided with the resources and funding they need to deliver timely assessments and ensure that those who need it receive the care and treatment they deserve.”
It's simply wrong to pick people with treatable conditions as collateral damage. Pushing vulnerable people further into poverty will mean they are more likely to deteriorate (needing more expensive care or longer unemployment) than suddenly finding themselves capable of work in a sustainable way, with an employer willing to take them on. Time will tell unfortunately but my feeling is this is the wrong approach and will lead to more costly issues, not less.