And where did the “Septuagint” come from?
From Jewish scribes who translated from the “Hebrew” texts.
Below is an excellent article on the preservation and transmission of the Scriptures down through the centuries.
http://www.defendingyourfaith.org/Old%20Testament.htm
The Dead Sea Scrolls have also served to show the accuracy of transmission over time.
Before their discovery in 1947, the oldest Biblical Hebrew texts were only about a 1,000 years old. DSS go all the way back to 200 BC. 1200 years earlier.
The great Isaiah scroll of the DSS is a nearly whole complete copy of the book of the prophet Isaiah.
Other than minor variants such as spelling or punctuation, the DSS are in sinc with the Masoretic Text. Serving to show the care taken in the transmission of the text.
Yet, the DSS are closer to the Septuagint than to the Masoretic text - and the differences are more than just spelling errors. I certainly agree the Septuagint was translated by Jewish scribes from Hebrew texts, but I don't see what relevance this has as to whether it is a more accurate source text than the BHS.