Is Macbeth an innocent victim of the powerful witches—nothing more than their plaything?
Macbeth is not simply the plaything of powerful witches. First, as we find out in act 3, the three witches who prophecy that Macbeth will become thane of Cawdor and king of Scotland are not all that powerful. When Hecate, the head witch, enters the scene in act 3, scene 5, she shows she is much more powerful than the others are, and she is angry at them for not consulting her before approaching Macbeth, as well as for, in her opinion, letting Macbeth use them. She states that they will have to regain control of the situation to destroy Macbeth.
Second, although Macbeth believes the prophecy that he will become king, nobody forced him to take matters into his own hands by murdering Duncan. That is entirely Macbeth's choice. In fact, Macbeth had decided not to murder Duncan until Lady Macbeth attacked his masculinity and persuaded him to go ahead with the plot. That, however, had nothing to do with the witches. It was entirely Macbeth's decision to follow through with his wife's commands, although one could argue she knew how to manipulate him.
However, on the other side, once Hecate arrives on the scene, and the witches make their final, deceptive prophecies about Macbeth's fate (such as that he can not be defeated by a man birthed by a woman), it could be argued that he is so mired in troubles that he has to rely on them, and thus he becomes their plaything.