No.
Did he seem like a born hedonist who just descended into depression and incredibly severe alcoholism? Yes.
I don't like being 'forum policing dude' but this is what the 'questions that don't deserve their own thread' thread is for, honestly.
Although this a sad conclusion, I tend to agree. No need to gloss over the evident fact that Dennis just couldn't say 'no'. To live in abstinence, even for a brief while. IMHO he tried all of the time to blot out the terrible abuse meted out to him by Murry, in his adult life. If he had a mental illness, it must have been post-traumatic stress disorder; not only war veterans have that.
And I am certain he suffered from strong guilt, because deep in his heart he may have hated his destructive lifestyle. That is why he also was uncommonly gentle and altruistic, giving. Which led to many an unexpected problem, not the least of which was his letting in the Manson 'family'.