The Jewish approach to this matter leaves out the need for faith, belief, and delusion. Why? Because we don't see these texts as historical reports.
They are liturgical narratives, texts designed specifically to be read aloud in formal public worship. They overlay a religious interpretation over our history in order to provide a moral lesson from reflecting on our past, but they are never understood as being either the true story or even the complete one.
Case in point: ever join any of your Jewish friends for a Passover Seder? At the dinner we retell the Exodus story from a book called the Haggadah. You might have noticed that the details of the Exodus differ not in a few ways in the Haggadah compared to the Bible book of Exodus. Why Moses himself is never even mentioned!
This is because our history and even our theology are separate from our liturgical texts, the Scriptures. While Jehovah's Witnesses believe that the Hebrew Scriptures are the theological and historical basis for religion, Jews see things in a completely opposite way: our religion is the theological and historical basis for the Scriptures.
Our theology, doctrine, and religious practices developed separately before, during, and even after the composition of many Bible texts. The Hebrew Scriptures are the "story" of what we believe, not the basis. What we believe was carried via the ancient practice of oral transmission, and this set of beliefs, doctrine and theology became the Mishnah. The Mishnah was later codified in the Talmud. The Bible contains the stories based on the religion in the Mishnah, not the other way around.
Because of this Jehovah's Witnesses have done you a disservice by teaching you that the battles and other narratives in our Scriptures are literal reports and thus the basis for theology and doctrine. Because the intention of the narratives in Jewish Scripture are to give a setting for the lesson to be preached at the worship service, battles of the past are retold in ways that teach what happens when we obey God and what happens when we ignore God. As you have noticed, sometimes the separate stories contradict one another. This is because they are divided into liturgical portions, the divisions of which are never included into Christian translations, and you are left without realizing that what was meant to apply just to the previous portion and battle does not necessarily have anything to do with the following one.
Lastly, most of the battles and genocide didn't happen at all. Our actual history as well as archeological research and DNA studies all agree that we gradually merged with the people of Canaan. We didn't conquer them. The battles and great slaughters are often symbolic of our desire to say we rooted out all that was heathen from our midst (though we really didn't). Sometimes, however, we were just as violent to some of our neighbors as discussed in the Bible and we probably did even worse a few times and likely left that out possibly as not to make us look bad, but for the most part you have been duped by the Watchtower again. These stories are not designed to be read separate from Jewish doctrinal sources.