Martin Luther is only mentioned because he was the most prominant revolter at the time. You use the words heretical cult...it was Luther who was the heretic. It is the prerogative of the existing church to determine what is and isn't heresy against them.
For the protestant revolters to decide that the true and only fully Christian church on Earth, Catholicism, is heretical is beyond bizzare.
Heresy is determined by those being denied the truth, not the deniers.