The answer is: The limits is that the Torah has high chances of having many stories over-exaggerated or a bit tweaked which does not make it a good historical source.
To be considered as a strong and reliable historical sources, it needs what historian called as a primary sources. Primary sources could be a set of documents, letters, pictures, or items that exist and directly involved in the historical event. There is no primary sources in the book of Torah, so it cannot be considered as a good historical source.
