As to the authors intention to show that the blood and lineage of the Jewish people is untainted, consider the fact that according to the Bible, Abraham and Sarah were brother and Sister! (Genesis 20:12.) This same author is the one who insulted the Prophet Lot by saying he had an incestuous drunken relationship with his two daughters, (Genesis 19:36) And Jacob was married to two sisters at the same time: (Genesis 29:28). The intention is clear, that the author of Genesis is either a pervert obsessed with incest, or he slanders honorable prophets with false stories of Incest in order to show that the blood of Isaac and his descendants (The Jews) is pure.
The fact that Jacob was married to two sisters at the same time and then their servant girls is much worse that Abraham involvement with Hagar. This would be a terrible case for the purity of Jewish people.
The author of those critiques just doesn't understand biblical writtings. What is being targeted here is not single individuals but sin in every man.
It is important to note that genealogical tracking did not start with Ismael and Isaac, but with Adam and Eve. I am not Semite, perhaps I should go after scribes for not tracking my ancestors and only focusing on the line of Shem...that would be simple paranoia.
What is being tracked in the Bible through genealogies is Christ; the pure seed or pure fruit of a woman.
God express his sacred creative power through human sexuality. It is through human sexuality that every man is created. But a corrupt seed means a corrupt tree, so if you need a perfect tree, you need a perfect seed which can not be corrupted. God promised this seed to Adam from the beginning as his pledge of his Mercy to Adam and Eve. It is this seed which is being traced throughout the OT by prophetic scribes. This seed finally came out through the fruitfullness of the Virgin Mary.
Muslims could be amont the first to realise this and rejoice over it considering what they believe about Jesus's conceiption and birth.
Otherwise, did the Jews also write the Quaranic verses describing the birth of Christ?
If Jewish Scribes were focused on exalting themselves and their ancestors, they would not point out their own sins. Instead, they would perhaps justify sin and call it lawful or permissible by God because ancestors/prophets did it. But they focus on God and his perfection and they don't seem to be afraid of pointing out that even great men were not perfect even if these men were their ancestors.