I agree that the character became a mess in the last few seasons. Apparently there was some behind the scenes stuff with certain writers(I think Behr and maybe some others?) thinking they'd gone too far in making Dukat complex and multi-faceted, so they decided to turn him into a more cartoonish and one-dimensional villain.(I mean, I don't think the memo was to literally turn him into a cartoonish villain, but that was the effect of the changes)
Yes. I agree completely. One gets the impression that the writers were uncomfortable with the popularity of a "villain", and engaged in an effort to make him more villainous, per se. The result was ridiculous. Why they would strive to do so in the first place is baffling to me, because a charismatic antagonist is what draws the viewers in...people like to be able to feel a certain degree of empathy with antagonists. It fascinates us, this pull of the forbidden. The moment the villainy is too cartoonish, it loses its magic, at least in my opinion.
...but then again, it was the 90s, and we all make mistakes.