Any narrative of a tribal confederacy evolving into a kingdom will appear legendary. They wont however present the bad as well as the good of their founders. When they do the bad isn't the unflattering kind you see in the David narratives. I can agree that the version left to us was redacted sometime from Hezekiah to the post-exile periods. We should remember this doesn't mean they were then created whole cloth. There's no problem positing the establishment of an Israelite kingdom around 1000B.C.. For this reason many minimalist scholars present King Saul favorably yet discount David. Because if there was no literal King David they would have to create a kingly character by some other name. An Israelite kingdom of some type was established around this time. The size was debatable only because of a lack of extant texts or monuments. Yet there are no extant texts, that I know, of the same period by other accepted entities. From the southern Sinai to the Euphrates. We can conjecture that it was roughly organized with an unstable central govt. This fits very well with the biblical narrative. The Bible describes no empire comparable to those north and south of Canaan. Jerusalem at this time was only a 25 acre plot of land. Yes, it was small, but not for the region. Hazor the large Canaanite stronghold was only 50 acres at the time. Laish, later Dan is the described northern extent of the Israelite kingdom. When Israel took territory by battle it wasn't incorporated into Israel but at best annexed for the purpose of tribute. It would never appear as an empire. The Bible doesn't present it as such.