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.