Interesting. I think theres a couple of really key points that are a little bit overlooked here though.
Its important to seperate design and art. Design is not art.
Design is creative problem solving. Sometimes that problem might just be “this needs to be decorative or beautiful” which is when design comes close to art, but fundamentally (for me at least) there is a a design needs to answer a question or a need in order to be valuable (and therefore good or even better, great!). Being depressed can be a distraction for many people, and a crippling disorder for many others. Its not just a case of “being in a bad mood” when you suffer from depression, it something that can dominate and disintegrate every aspect of your life, absolutely including your day to day work. With design, you have a goal that needs to be completed. Just the same as if you work in an office and need to complete an excel spreadsheet by the end of the day, depression can also stop you from making a really great excel spreadsheet.
Art however does not have that prerequisite. Art can exist to create more questions than it answers, or for make us feel a certain way or think about a certain thing, or just for the sake of existing. That is why artists (and by artist I someone whos creative output is not design, whether they be painter, writer, musician, whatever) who suffer from mental health issues and allow that to be present in their work are able to create great art which comes from that place in their mind. Sylvia Plath is a great example.
But thats not because being depressed made them great artists. Its because they were great artists who made great art out of depression.
And, lets be very careful here not to confuse depression with “having a bad day” or what it means to be “suffering for your art”. Depression is a severe and serious mental health condition. Its not something that the sufferer chooses to be or switch on or off at will.