Your charge is totaly and absolutely false in its entirety!!! Either you don't understand PSA or you don't understand the works of the Devil - it is either one or the other and most likely both! PSA deals with the very root of Satan's works and destroys the very goal of his works. The root of his works is sin and the very goal of his work is the destruction of the human race. Without PSA Satan would be victorious.
The atonement is ONE act with MANY aspects (that is where we deny, not that it is many acts).
However, your claim that Penal Substitution states that the purpose Christ came was to defeat the works of Satan is false. Scripture treats it as a primary purpose. The Theory treats it as secondary to addressing the penalty of sin itself. Same with interpersonal sin. Same with sin as it relates to the Kingdom.
My point is that you cannot focus solely on one aspect and then pretend you've addressed the whole thing by implication.
"The doctrine of penal substitution states that God gave Himself in the Person of His Son to suffer instead of us the death, punishment and curse due to fallen humanity as the penalty for sin."
What does that say of the Kingdom? Nothing. What does that say of defeating the work of Satan? Nothing. What does that say of interpersonal sins? Nothing. What it addresses is punishment due man as the penalty for sin. It does not even address sin as a power (which is how Christ addressed sin the most).
Your error is not in what you affirm. It is in what you seem to believe is secondary. That colors what you affirm.