Light immunes aren't the bottleneck they once were with this extra pierce. I think fb/hydra smashes any flavor of nova if you're pack hunting in stony tomb or herald hunting. Pack hunting in stony field or full clearing flayer jungle? 200 fcr nova takes the cake. Tombs? Probably self infi wins there. Pack hunting chaos? I think 200 and 105 nova are tied and outclass any fire build there.
Btw I use ES even with 1 pt ES, 1 pt telekinesis on fire sorc, and go half life half mana
Say TZ 96 tombs. Very generous area, only native immune are scarabs and they are fairly low hp less than 100% multiplier, and in P8 the champion/unique scarabs are 60.4k hp. Heralds can be as high as 906.4k
So the regular immunes champ/uniques about 4 seconds to kill in full pound town, but heralds as much as 60 straight seconds of DPS?
I mean, that's not even the worst case, and assuming your merc somehow lives. There are plenty of 200%+ hp packs like urdars and venom lords and unravelers and blood lords who will be lightning immune with lightning enchanted, or as little as magic resistant like venoms. And they're also pretty good at instakilling your merc (and pretty threatening to -you-). Even just non-TZ infector of souls has 128k hp and spawns immune with either affix and then its about 9 seconds to kill him and that's just one monster, granted your merc can actually do work against venom lords unlike urdars/blood lords/heralds. If its a pack of TZ96 herald p8 frenzytaurs I guess you just hit save/exit as fast as possible but fire isn't that far behind