I have been aware of the existence of the Manichean Heresy for at least 50 year, along with the Albigensian Heresy and the Arian Heresy. A few years ago I read a historic novel about the end of the Roman Empire in which Arianism figured prominently. I have forgotten the details and title of the book but basically it covers the rise and rule of a Gothic king/emperor who was an Arian and tried to save the Roman empire from its weak and dissolute leadership which suffered and cracked under the assaults of Attila the Hun and Alaric in the 500s AD. He was forced out of Italy (Ravenna?) and set up rule in what became France and had serious run-ins with Genseric, a Vandal who ruled in north Africa.
Arian Christianity was a much more tolerant form. It was tolerant of other brands of Christianity and was more friendly to women, among other things. The Roman church was successful in destroying Arianism, Manichaeism, and other offshoots of Christianity except for the Eastern Orthodox form. That whole period is very interesting.
You need to re-read your history.
Three was no “Eastern Orthodox” form until the schism created by crowning Charlemagne “Holy Roman Emperor.” Until then the Emperor of the Easter Roman Empire was titular head of the Church. Authority was divided between multiple sites such as Constantinope, Antioch, Rome, etc.
By crowning Charlemagne emperor and claiming primacy, Rome split the Church.
I decided to do an additional check on Genseric, also called Gaiseric, the Vandal king. He had an extremely successful and long lasting rule, but when he died named his oldest son king in the Roman manner, rather than have the army elect the king in the Germanic manner. This son was a brutal tyrant and led to the fading of the Vandal success and perhaps their bad name? A very interesting read of a complex time in changing empires and powers. Constantinople was already acting quite independently of Rome although the schism in doctrine had not yet occurred.
http://homepages.rpi.edu/~holmes/Hobbies/Genealogy2/ps15/ps15_208.htm
Also, I wouldn't say Arianism was a "more tolerant form" -- Arianism is similar to what the Jehovah's witnesses now believe, namely that Jesus is a "lesser" god, not of the same substance as the Father.
Sorry, you ascribe too much to Rome.
Before the 12th century, the majority of heresies and splits occured in the East
you had the Coptic and Ethiopian Churches breaking away after Chalcedon
you had the Syrian Oriental and the Armenian Church breaking away
And you forget the 1000 lb gorilla -- the ancient Church of the East or the Assyrian Church -- which, in the 8th century based out of Ctesiphone near Baghdad was larger than Rome and Constantinople and had 1/3rd of ALL Christians in the world as adherents and was spread from Ctesiphon to Mongolia (Genghis Khan's wife was a Naiman, a Christian mongol tribe) to China and to India (the Marthomite church in Kerala)
And what about the Mandaean heresy in southern Iraq?
Also, Arianism, Apollinarius etc. arose in the East -- because the East was much more erudite, more scholars etc than the West
Rome "destroying" is quite the exaggeration -- the Cathars were clearly gnostics, not Protestants (who hold to the Nicene Creed)
And Manichaeism, as I pointed out above was not an offshoot of Christianity anymore than Bahaism -- it was a syncretic religion