The Book of the Zohar

Rabbi, greetings and blessings,
 I am a student in a Lithuanian yeshiva, and I am turning to you regarding a matter that has been troubling my peace of mind for many long months. It concerns the status of the teachings of Kabbalah — the Book of the Zohar, and the movements that branched out from it (Hasidism and the kabbalists of our time).
I was educated to believe in the Torah that is transmitted through a pure tradition, generation after generation, from teacher to student. In the revealed Torah — from the Mishnah, the Gemara, the Geonim, and the Rishonim — we have a proven historical continuity, reliable manuscripts, and open discussions that do not depend on a single individual.
 By contrast, in the teaching of the “hidden” we encounter a puzzling phenomenon: suddenly, at the end of the 13th century in Spain, a comprehensive work appears, unknown to any of the earlier Rishonim or Geonim, and it is attributed to the Tanna Rashbi, who lived about a thousand years earlier, without there being any clear trace of this in the writings of the East or among Rashbi’s own disciples.
 The origin of the book is centered entirely around the figure of Rabbi Moshe de León. In Sefer HaYuchasin by Rabbi Avraham Zacuto, the famous testimony of Rabbi Yitzchak of Acre is cited: he met the widow of Ramad, and she testified in her own voice that her husband wrote the book from his own mind for the purpose of earning a livelihood, and attached it to a great tree.
Beyond the historical testimony, the book itself is filled with internal evidence of its late origin:
Anachronisms: names of Amoraim appear in it who lived hundreds of years after Rashbi.
The language of the book: linguistic scholars (and authors of books such as Mitpachat Sefarim by Yaavetz and Vikuach al Chochmat HaKabbalah by Shadal) have shown that the Aramaic of the Zohar is artificial Aramaic, interwoven with the syntax and concepts of the Spanish language and medieval philosophy, and is unlike the Galilean Aramaic of Chazal.
Misquotations of verses: the book quotes phrases with the wording “as it is written” that do not exist anywhere in the Tanach, or it distorts existing verses (such as the quotation in Part III, 244: “as it is written: Hear, surely hear, my lips trembled,” which is not a verse in Scripture).
But the greatest concern is in the realm of pure faith. The concepts brought in the Zohar appear, from a rational perspective, to contradict the absolute unity of God taught by the Rambam. The division of Godliness into ten Sefirot, the conceptual split between “Kudsha Brich Hu” and “Shechintei” as two forces supposedly operating separately, and concepts of “zivugim” in the upper worlds — all these arouse a difficult feeling of the introduction of foreign ideas, disturbingly similar to Christian theology.
History shows that once the book was accepted, it became forbidden to question it, and anyone who dared to challenge it was censored and persecuted. This happened, for example, to some of the sharp words of the Noda BiYehudah (Mahadura Tinyana, Yoreh De’ah, siman 93), who spoke out against the mystical practices of the kabbalists of his generation and called them “a spreading plague,” words that were censored or blurred in later printings.
In addition, this platform gave rise over the generations to extreme movements: from Sabbateanism to modern distortions. In Hasidism (and particularly in Chabad and Breslov), the concept of the “tzaddik” was introduced as a necessary conduit for the service of God — an outlook reminiscent of the generation of Enosh, who interposed mediators between man and God, and it grants rabbis absolute power that at times uproots the fundamentals of Halacha (as can be seen in extreme sects in our time, such as “Lev Tahor” or Berland’s followers, who draw legitimacy from the self-glorification of the “tzaddik” that appears in the Zohar).
Even the mystical descriptions of the Baal Shem Tov (such as the ascent of his soul, his meeting with the Messiah, or his learning from Achiyah HaShiloni, who lived thousands of years before him), or the somatic and puzzling descriptions in Sefer HaChezyonot by Rabbi Chaim Vital, seem like a copy of stories about false prophets from other religions.
My great question is: how was this accepted in this way among the Jewish people? How did it happen that Rabbi Yosef Karo, who himself was captivated by the teachings of the hidden and testified in Maggid Meisharim about an angel dictating his way of life to him, became the definitive halachic authority, and even inserted into the Shulchan Aruch rulings whose source is solely the Zohar (such as abolishing the laying of tefillin on Chol HaMoed, a custom that has no source in the Gemara or in the rationalist Rishonim)?
It is very difficult for me to observe laws whose source is not in the clear halachic tradition, and I find peace only in the clear and true way of thinking of the Rambam in the Yad HaChazakah and the Moreh Nevuchim. Why did today’s Lithuanian community, which in the past waged a fierce battle against Hasidism and the changing of customs, ultimately adopt the kabbalistic conceptual world and stop fighting for the original rationalism?
I would be very grateful for your enlightening response.
With great respect and in anticipation of an answer,
David

Greetings and blessings 

The reason that the Book of the Zohar was accepted in the Lithuanian community is apparently based on the Vilna Gaon and his disciples [Rabbi Chaim of Volozhin, Rabbi Yitzchak Isaac Chaver, and other great Torah giants], whose critical discernment and absolute precision regarding every detail no one questioned. And they gave their endorsement to the Book of the Zohar.