Evil vs. Good
Even before we get to the Gospel, we must clarify that "Supreme" does not apply to "evil" the way it does to "Good". As Lewis would say, Satan is the opposite not of God but of Michael. Whatever sort of "being" or "existing" one would attribute to God cannot be attributed to evil, because evil is all about non-being and privation of good.
What's good about the post is that it says that well. The Supreme Evil is not a thing in itself (Or, as we say in German, the ding-a-ling an sich, it is the loss of the Supreme Good.