Me neither. Energy regen definitely isn’t the problem. The Arcanum Dusts I was experimenting with were for DA mainly, not regen.
Could be an idea. Problem is: Why would you use FOI on a Purifier, if you can get Firestrike and all those nice WPS skills and synergies plus a shiny, powerful gun?
Nevertheless it might be worth a try: BWC, RR from Thermite mines, Blast shield for survival, damage buffs from Flame touched and Vindictive flame, maybe find a way to convert damage to fire + lightning only… Guess I’ll try it if I find time.
OFC, you could also go Paladin. This build by omnitrio basically still works.