How do you come to the conclusion that the Jews were absolutely perfect in their translations?
You rely on what you claim to be perfect. Not so.
The arguments; "O.K, the New Testament is not reliable, but the Old Testament, which is much older, is also not reliable", or the argument; "The Jews changed the Old Testament after the rise of Christianity, in order to discredit Christianity" are not valid. The Torah, the most Holy part of the Hebrew Bible, is transmitted through the ages, over a time period of 3300 years with an astonishing degree of accuracy. There are very many rules that apply to the copying process of Torah scrolls: They may only be written on parchment of kosher animals, which must be sewn together with tendons of kosher animals. It may only be written by a Jew, dressed in a Jewish garment, in a state of ritual purity, which means that, amongst other things, he must wash himself in a ritual bath. Even his state of mind is subjected to certain rulings. The whole manuscript must be ruled before it is written upon, when three words are written without ruling, the whole manuscript is disqualified and must be buried. The ink may only be black, prepared according to an ancient recipe. The Torah scroll may only be copied from another authentic scroll, and absolutely no deviation is allowed. Absolutely no words may be written without first looking to the example. The length of each column must be between 48 and 60 rules, and the width must be 30 letters. Between the letters must be a space as wide as a hair, between the paragraphs a space of nine letters, between the books a space of three rules. Calculations have been made how many letters there are in the whole Torah, which letter is the middle, how many letters there are in every book of the Torah, how many times certain words and even letters appear in the text. And there are many, many more rules for copying Torah scrolls that are still in effect, up to this day. No other religion had such an extremely precise way of copying their holy texts. This shows the enormous respect that the Jewish people have for the sacred text, and this is the reason that the text is handed down through the millennia with an extreme grade of accuracy.
You know anybody else who transmitted their holy books like this?
The NT is based upon the corrupted LXX, because the NT writers couldn't read Hebrew. So they had to use a bad translation.
And then saying: "Look! The NT is in agreement with the LXX, and the Hebrew text differs, therefore the Hebrew text is wrong!" is of course nonsense.