Tabitha doesn't have a split personality... She is robosexual and xenophobic.
The Split personality is with Lily, and it's not even played in a cliche manner, it's Lily's deranged mind giving her a coping mechanism for the violent things she did for the Master as she was a Sweet old lady before getting dipped.
I don't see how that's comparable to a cliched "I am fro ma brute race but I learned shakepseare so now I am good" and a Mutant with Glasses and a Scarf...
I guess that's fair enough but she talks to herself in a voice of another entity, that's basically a split personality or schizophrenia.
Do you think Lilly isn't cliché? That has been done a thousand times before, it's the plot of a lot of things in history. This is my point. You can't call everything cliché because you dislike it.