It seems to me as though a straightforward desire to manipulate the audience's response at all costs
had taken over towards the end.
The writers made no secret of the fact that they were troubled by how popular the character had become.
Whether novel or screenplay, once you put your work "out there" it's no longer entirely yours; and while your public may react to a character you've written in ways you didn't intend and may dislike, you have to leave themthat freedom.
I think it all became an incoherent mess because the writers got so hell-bent on forcing the viewer to react to the character the way they had decided the viewer should
react, "if this tack doesn't work, let's try yet another..."
Then they just went further and further o.t.t. with it until they'd screwed up a well-realized, believable, complex antagonist into a caricature of evil spouting portentous rubbish.
It was like watching someone carefully draw a picture with every detail shaded in, and then slash across it with a big slopping paint-brush.