As much as I dislike the guy and his work I wouldn't go so far as to say he is mentally ill. If there is anything that can be attributed to Ken is being a textbook example of Dunning-Kruger due to his lack of self awareness regarding his own skills. He believes himself competent and knowledgeable yet lacks the meta cognition necessary to recognize his own incompetence as an artist and a writer. It is a cognitive bias for sure but that's about it. Ken suffers from having low standards and being too arrogant for his own good. He is a failure because there is no humility to recognize how poorly made is his work and that there is a need to learn to improve said skills.
If anything he is an Andrew Dobson that managed to achieve a modicum of success by landing a job on a company that itself was too incompetent to realize the lolcow they had hired.