I would tend to be sceptical of the idea of any link between Catharism and French Protestantism as, even discounting the beacheads Protestantism made in Northern France (as one could argue that some Dualist sects where likewise present in Northern in the High Middle age), the geographic discrepencies are simply too large.
Catharism never made any serious headway in Gascony, appart for Quercy and Agenais who where culturally and politically linked to the Languedoc during this era, let alone north of the Loire in Poitou and Saintonge, while both regions where central to french Protestantism. Protestantism also managed to establish a presence in Provence and in the Rhone Valley while Catharism never did.
On the other side of the equation, the Lauragais and the Toulousain, who had once been the homes of strong Cathar churches, where pillars of the power of the Catholic League in Southern France during the French Wars of Religion. Catharism also managed to establish some presence in Catalonia, while Protestantism never took off anywhere in the Iberian Peninsula.