Does the Orgegrowth's Challenge talent prevent opposing units within its effect range from using instead of attacking talents like Weak-point from the hammer and chisel equipment?

Challenge says that any Attack a Hero makes must be against this Unit. Weak Point is itself not an Attack, but it is instead of attacking. As a result, because the Hero loses its ability to Attack it cannot use an instead of attacking Talent unless that Talent was directed at the Orgegrowth because the Hero can Attack it.