I've spent many a year back in high school drawing rather dark and disturbing images (at least by the commoner's perspective), not to mention my written works took a similar theme . . . and I've turned out just fine . . .
. . . and the countless other "professionals" who's work is known for that darker edge (i.e. Giger) have been fine, too.
Although artwork, poetry, or any other creative release can possibly be a reflection of an individual's emotional or mental state - it can't be taken as definitive without actually having the individual undergo a full psych evaluation. There are too many people who might express themselves differently from how they actually feel, and their creative release will take no similarity to what's actually going on inside their head. There might be some similarities with specific individuals, but the majority of the time there's not. It's a big reason why psychiatrists focus more on someone's interaction with other people and with social groups, instead of handing them some paper, a bunch of crayons and telling them to draw whatever pops into their head.
You're critic is, for lack of more appropriate terminology, full of horse-shit.