Having God and the devil as evenly matched but opposite powers is not something you would find in theology. Learn the basics of it before thinking you have created a proper critique.
That is completely irrelevant. The ontological proof claims to deduce the existence of an entity from a definition of that entity. It does not matter whether this definition happen to match some current religious dogma or not.
It's not the most interesting argument for God I've encountered, but it's not trivially invalidated by elevating evil to the same status as good. That hasn't been a serious element of any real theology since long before the ancient Hebrews.
Theology is the art of imagination, the same way that politics is the art of the possible. Imagining absolute evil is only interesting when you want to attack the idea of absolute good. Absolute good remains interesting without a foil. So therefore people will be willing to believe in it.
This property is not shared by things that are not God, such as Santa Claus. So you can't use the ontological argument for God to also show that Santa Claus exists. Santa Claus isn't the greatest thing ever, so Santa Claus isn't bound by the rules of logic to exist.
"The spaghetti monster, by definition, is that for which no more delicious thing can be conceived. The spaghetti monster exists in the understanding. If the spaghetti monster exists in the understanding, we could imagine it to be even more delicious by existing in reality. Therefore, the spaghetti monster must exist."
Think your argument through first. Are your premises actually true?