In essence, Protestant Buddhism is a form of Buddhist revival which denies that only through the Sangha can one seek or find salvation. (source)
Orthodox Buddhism, especially Theravadan, holds that only within the Sangha (that of the ordained monks) can Buddhism be taught. The orthodoxy does recognize the existence pratyekabuddha yet denies that such Buddha is Sangha or is able to teach.
Japanese Zen, an Orthodox Buddhist sect much in the shape of the old Catholic church, views that only the ‘Zen Priest’ is Sangha, and only their priest can attain enlightenment and teach. Those apostates that teach Buddhism and Zen outside of the church are viewed as ‘disloyal’ to be not only disassociated from, the Laymen are encouraged to shun the disloyal.
Buddhism never had a Protestant reformation, there is no equivalent to Martin Luther though some may point to the Chinese monk LinJi (Rinzai) and his “Man of no position” rebellion as a type of Protestantism. Whatever LinJi intentions were at the time are now moot, whereas his lineage marched right back into the orthodoxy that LinJi rebelled against.
To the Asian Buddhist Churches, Protestantism is a foreign view and most unwelcomed. Tibetans hold to a Religious royalty in where leadership and succession an oligarchy that simply declares a child to be a ‘Reincarnated teacher or emanation of a diety’ and brings those children inside their church to be indoctrinated into their ways and customs.
Therevada is instant that only the bhikkhu (A ordained male) can be a Sangha member, and all others are Laymen who serve the bhikkhu. In Theravada, only the bhikkhu can teach Buddhism and speak Dharma, for laymen to do such would be seen as heretical and blasphemous.
In the Zen sects, the adoption of the ‘Holy Lineages’ in where oaths of obedience and loyalty to the sect are held sacred that are made by the Preist who demonstrate loyalty to the sect, and it is viewed that only those priests are Sangha, and only they can teach Zen/Buddhism and speak Dharma, and view laymen in the same way as Theravada.
Buddhism coming to the west was not prepared for the Protestant mindset of the modern westerner. The publication of sutras and zen text in English, which once were only found in the sect temples and accessible only at the pleasure of the priest, has accelerated a Protestant view of zen much to the chagrin of the orthodoxy of Buddhism.
ZCLA, NYZC, and SFZC attempt to emulate the Japanese orthodoxy, though are only seen as Laymen LARPing (Live Action Role Playing) in Japanese robes by the Asian Orthodoxy and not considered Authentic or Authorized.
Other Western Zen schools, like Shasta Abbey, attempted to bridge the orthodoxy and Western Protestant views with the creation of the Layman-Priest. Jiyu Kennett, an English woman who was both ordained in China and Japanese Zen, created her Buddhist Priory and Zen Vicars and designed a uniform that was a hybrid of the Chruch of England Minister and that of a Zen priest.
Other movements in the west, such as Dark Zen, squarely criticized orthodoxly Buddhism, and especially the Western Zen centers who were clearly LARPing as Japanese Priest, in saying that the Holy transmission is between YOU and the COSMIC BUDDHA, and not as vows of obedience and loyalty to a sect.
Like it or not, the Protestant Reformation of Buddhism is happening. Movements like Secular Buddhism are absolutely part of the Reformation, as is Dark Zen and many other Buddhist groups who organize much like the American Christian Churches with Ministers who simply read the English translated Sutras and Zen books for themselves and minister to the population the message of the Buddha.
Liken to the struggles that Christian Protestantism had with the Orthodox Catholic Church, Western Protestant Buddhism is moving forward and shaping to become dominant over the orthodoxy.