Most likely, Bruce Metzger is right and you are speculating baselessly.
I've read Metzgers's opinions on Lamsa, and noted his usage of strawmen and ad hominems. George Lamsa was rather open on his choice of Syriac manuscripts:
"George M. Lamsa, the translator, devoted the major part of his life to this work. He was an Assyrian and a native of ancient Bible lands. He and his people retained Biblical customs and Semitic culture, which had perished elsewhere. With this background and his knowledge of the Aramaic (Syriac) language, he has recovered much of the meaning that has been lost in other translations of the Scriptures. There is a section on the problems of translating from the Aramaic to the Greek. Manuscripts used were the Codex Ambrosianus for the Old Testament and the Mortimer-McCawley manuscript for the New Testament. Comparisons have been made with other Peshitta manuscripts, including the oldest dated manuscript in existence.
The term Peshitta means straight, simple, sincere and true, that is, the original. Even the Moslems in the Middle East accept and revere the Peshitta text.
Although the Peshitta Old Testament contains the Books of the Apocrypha, this edition has omitted them."http://www.tyndale.cam.ac.uk/Scriptures/LBP.htm
"Manuscripts used in making this translation were the Codex Ambrosianus for the Old Testament and the so-called Mortimer-McCawley manuscript for the New Testament; the former is in the Ambrosian Library at Milan, Italy, and has been identified as fifth century A.D.; the latter was used for our previous translation of the New Testament, of which this edition is a revision, and has been variously identified as sixth or seventh century A.D.Comparisons have been had with Peshitta manuscripts in the Morgan Library, New York, N. Y., with manuscripts in the Freer Collection, Washington, D. C., with the Urumiah edition, and with a manuscript of the Peshitta Old Testament in the British Museum, the oldest dared Biblical manuscript in existence. Our translator states that comparisons show no differences in text between these various manuscripts, and that he has filled in the few missing portions of Chronicles from other authentic Peshitta sources, as noted in his Introduction."http://www.aramaicbiblecenter.com/lambib.html
Metzger either intends to deceive, or he has no real idea of what he's talking about. Metzger himself is somewhat of a controversial figure, but you won't find me using that alone as an attack against him.
My copy of the Lamsa Bible even has pictures of the manuscripts which Lamsa utilized. Why would you use Metgzer as a source, without even looking into it first? Why would you be speculating baselessly?http://www.aramaicpeshitta.com/Online_Version/greek_primacy_deception.htm
It is obvious, however, that he is a figure of controversy, and something like 3/4s of the websites I found mentioning his translation were woo-woo, not really Christian sites.
Does that have any bearing when it comes to the rules of logic? If the authority of Jesus Christ were dependent upon the behavior of his followers, what authority would he really have?
For sites related to George Lamsa which are not "woo woo," I'd recommend www.Peshitta.org
I see no evidence that the Malankara Orthodox Syrian Church uses Lamsa's translation.
It is not endorsed by the Malankara Church, it is just the only complete English translation available. Though imperfect, it is still considerably better in many ways than Catholic or Protestant Bible versions.