The tradition's authority rests on a small number of manuscripts. One tenth century codex was regarded as the most accurate and was used as a reference for centuries, and a large part of it was lost in the twentieth century, leaving a mutilated witness. Another complete codex, explicitly dated by its scribe, survived intact and is the basis of the standard printed critical editions, which is why an eleventh century manuscript in a Russian library underlies most modern Hebrew Bibles. The text those manuscripts carry is not the only ancient one.
The Greek translation made in antiquity sometimes reflects a different Hebrew text, and the scrolls recovered from the Judaean desert include copies agreeing with the Greek against the received Hebrew, as well as copies agreeing with the received Hebrew, and others agreeing with neither. Textual variety before the standardisation is now a matter of physical evidence rather than inference. That changes the question.
Where the traditions differ, in the book of Jeremiah most dramatically, the argument is over which text is older and how the difference arose, and it cannot be settled by appeal to the received text's accuracy, which is not in doubt. The Masoretes transmitted their exemplar with great precision; what that exemplar was is a separate matter.