No one has ever answered me that on a rational level.
I did on another thread, but you probably didn't notice. I said that Gnostic-like Christianity, such as illustrated by Johannine and Pauline literature in the NT, would escape your double syllogism easily as it holds the OT as an "inferior revelation" at the very best. This is especially true of Marcionism, which rejects the OT altogether. Interestingly several scholars consider Galatians as a Marcionite production (note 3:19f: " Why then the law? It was added because of transgressions, until the offspring would come to whom the promise had been made; and it was ordained through angels by a mediator. Now a mediator involves more than one party; but God is one." What is inferred is that the Torah doesn't adequately express God's will.)