not sure if he’s overtrans player. asked him some time ago about his gear no reply yet.
AFAIK it’s sacrificial build, much like of their Kriv3 who went Priest2 at Rank8. wherein that pyro goes necro to amp their main DPS (SR) from the decay bonus amping +200% more damage on missiles.
if you recall my scout3 thread, we do run the same comp with Scout3 cannoneer, hitting at most 30-40k split shot due to decay.
but well, i don’t know anything here because i’m a clueless player 
edit1: who ever told you that Sorc was for SP regen is too damn retarded, melstis can be kept at max duration with sp pots (keistas), and necro does 200% bonus for missile (NOT 100% FFS you cluess bastard
) which is decay from pole + decay from shoggoth.
but don’t believe me, because i’m a clueless guy 