Privation of things is equal to the privation of good, while privation of things means nothing and privation of good means evil, we can thus conclude that evil means nothing. If evil means nothing, evil doesn’t exist. Therefore, it seems that from Descartes response, there is no necessity to discuss whether God creating of letting there be evil in the world.
When looking at Descartes’s whole response, his response to this problem of evil is an external critique. In his response in this question, he is evaluating his statement by using the other fact that outside of his original statement. For example, the fact that evil exists dismissed the statement that God created all goods is an external critique since he is not judging the logic within the sentence that God created all good, but used another fact to defeat it.