While I agree, and while I think she's had the potential to be a tyrant for years, it's worth considering that she's as much a product of her experiences as Sansa. Both were sold into marriages, both were, effectively, raped on their wedding night. That Dany came to love her husband possibly just makes her assault all the creepier. (I'm trying to remember but wasn't their wedding night in front of all the Dothraki as well!) She then lost not only her husband but her unborn child.
I think it's highly likely she'll go off the rails now. Look what she's been hit with in close succession. She's lost Jorah, Missandei, two of her three dragons (who lest we forget she considers her children) discovered her lover is actually her nephew and has a better claim to the throne than her, plus far from being welcomed with open arms the people of Westeros seem quite luke warm when it comes to her. In many ways all she has left is the throne. It's become an obsession, no scratch that, more of an obsession.
Say what you like but protagonist or antagonist she's a fully three dimensional character and however her story goes it'll make sense from a certain point of view.