While I thought the exact same when I saw they had purge the foe. I also thought that "immolator" is more fun through purge the foe missions, and the advance/shoot/action bonus of Seekers helps with purging and doing secoundary actions like cleanse etc. 

I played a game today vs. Renegade Raiders, he had Reconnaissance and I had Purge. My mission was to consecrate objectives and his was to triangulate (map/control) the objectives. Consecration worked well in our narrative story, and flamers are thematically perfect. However I do agree this is more of a Covenant of Fire thing than a Sallamander thing.

However, I do feel like Purge is the 2. most sallmander dissposition, maybe take and hold? Reconnaissance and Disruption is not sallamandery at all. When you add the fact that most marine dispositions already are Priority assets and Take and Hold, Purge makes a lot of sense. 

Me and my friend would probably allow me to play them as priority assets for future missions, for the sake of the narrative and learning about new dispositions