I think you missed the point. The argument wasn’t precisely new when he made it, what was new was his use of Aristatilian logic to “prove” the existence of God. The proof requires that God be singular thus the god of the Islamic world (also the Jewish). The tri-part God of the Christian religions is therefore a corruption.

The video doesn’t really do a good job of covering the importance of his argument in the history of philosophy.

As an atheist, I don’t find the argument itself very compelling. The historical context is quite interesting.