Absense of evidence equals legend?

In a Nature article in May Haim Watzman writes

One way to experience the Elad view of the City of David is to tour the site with an Elad-trained guide. It is possible to visit the excavations on your own or with a guide you've brought yourself. But the default option for tourists and school groups is to hear the narrative that asserts the Jewish claim and historical connection to the site, say Greenberg and his colleagues.

There is some truth to these claims, as a Nature visit to the site suggests. The tour guide provided by Elad was well-spoken and knowledgeable, but mixed myth and fact in her presentation. For example, she asserted that the reason David chose the site for his capital is that it lies just below the Temple Mount, which is identical to Mount Moriah, the site where, according to the Bible, Abraham took his son Isaac to offer him as a sacrifice to God. Although the identification of the Temple Mount with Mount Moriah is well-established in Jewish tradition, there is no archaeological evidence for Abraham's presence on the site — or indeed for the existence of Abraham and Isaac.

In fact, a handful of archaeologists go so far as to say that David and Solomon may also be largely mythical characters. This view is rejected by most experts on the period — they tend to agree that it is likely the two ancient rulers did reign in Jerusalem. But many scholars argue that the evidence discovered so far — both at the City of David and at other sites in the region — indicates that the biblical description of the extent and wealth of their kingdoms is exaggerated.

Besides the interesting assumption that a Nature writer is the unbiased judge of a archaeological/ tourist guide (which may or may not be valid), how exactly has the guide mixed myth with fact?

Identifying Mount Moriah with the Temple Mount is enough for a fact for Watzman because of tradition (and presumably some archaeological data) and because many archaeologists happen to think there is some substance to idea that David and Solomon existed; but Abraham is a myth because of lack of archaeological evidence?

Then what of the well-established Jewish tradition for the existence of Abraham and Isaac? Since when is lack of a specific type of evidence evidence of myth? And what specific archaeological evidence does one expect to find for a specific individual that lived 4000 years ago?

Documentary evidence is strong evidence and the Bible gives documentary evidence that Abraham existed. Abraham is discussed in the genre of historical narrative. His ancestry, geography and activities are well described. His behaviour, both good and bad, are mentioned which can only add to the authenticity of the accounts. Moriah is even mentioned by name in connection with Abraham.

He said, "Take your son, your only son Isaac, whom you love, and go to the land of Moriah, and offer him there as a burnt offering on one of the mountains of which I shall tell you." (Genesis 22)

With regard to his slight on David and Solomon, a reading of opinions concerning the existence of Nineveh and Babylon from a century ago should caution men against having too much faith in "scholars."