Read the book "Pilgrim Church" by E. H. Broadbent to see just a part of the history of independent churches from 500 to 1500 AD in places like the Middle East, Central Asia, China, the Balkans and Europe.
In addition, calling the Albigenses "Bible-believing Christians" is just silly. They were none of those things.
There have been heresies and offshoot sects all over since Pentecost. The common characteristic of them all is that they have no common characteristics, not that they were proto-Baptists.