This is interesting. My T has similar thoughts on this subject. He doesn't think that framing problems as "mental illness" is necessarily helpful.
My T gave the example of a publicity campaign here in the U.K. Called "1 in 4", which is about de-stigmatising mental illness and making it accepts to talk about - it says that 1 in 4 people will experience mental illness at some point in their life. But my T was saying that 1 in 4 works as a publicity campaign and is a number people can get their head around, but a colleague of T who works researching this kind of thing says the real figure should be 1 in 1 i.e. everyone. T explained they mean that experiencing anxiety, depression, some obsessions, and other things, are all part of the human condition, that everything is on a spectrum, and when a certain issue gets quite far down the spectrum to the point that it is having a serious impact on someone's quality of life over a period of time then that is when we would label it as "mental illness".
Obviously it's a complex topic, but I do find this approach helpful in how it helps to "normalise" things and reduce stigma. I like thinking of the 1 in 1 figure, because I have had colleagues in the past who had a mind of macho attitude and claimed that they NEVER got physically ill - clearly, they were partly lucky and healthy individuals, but it was always clear to me that they were human beings and not comic-strip super-heros: if you are human, you can catch viruses etc. , to claim otherwise is just silly and it's a kind of macho posturing. I find it helpful to see things the same way when it comes to mental health.