I did say I was probably biased

(I suppose you might have missed my edit). But you are right about the book timing vs the film timing. Though I should have been more clear about my view of him in the films

. After Boromir dies in the film, we see Denethor as losing it but not completely lost, but enough to lose his grip on how to stay in charge of things and becoming even more of a...erm...certain part of the anatomy. Then he really goes insane after Faramir dies.
Anyway, I defer to you (somewhat regarding the timing of events) on how he is portrayed in the books. But he's still a jerk either way

.
GB