OT is not about a rainbow world, not even an ideal but possible world.

Old Testament reminds us that the normal humanity state is eternal tribal genocide, sometimes with larger or smaller tribes.

that we have risen, partially, and temporarily, above that, is a hard achievement, which is also hard to maintain. And Christianity is mostly responsible for that.

The difference Bible x Koran is that OT is not always normative. Just because OT Jews did shit, it does not mean we have to follow, or that they are an example. Even WHEN the violence was justified in a tribal context (and a lot more violence is necessary for them), it does not mean it is just for us. The Church is there to interpret the Bible anyway.

But in the Koran, every act of violence was performed by the perfect man leading the perfect state, the example to be followed to the letter until the end of the world.