I did level feedback sorc untwinked.
My goal was to build it around mana sweep + antimass.
Little tip, try to reroll blue circlet with psicrown oskill, if you are leveling any full energy character. It is complete ownage during leveling. Normal with no magic immunes, you wipe screens faster than anyhting ive seen. Act bosses die in ~1-2s. Skill has also huge mana costs, so plays well with mana sweep.
Later on when you get mana sweep to no cooldown, and pump that total mana, it is possible to 1 shot enemies with it during leveling. Antimass -> mana sweep. Later I got lucky found ele set gloves (40% max mana), made ath chest with more max mana, I was able to 1 shot elites while going through destruction. It was really fun and smooth leveling, very cool when entire screen dies in 1 cast. And you can rotate antimass combo every ~3s at this point.
For early bosses, had to use immersion to have enough burst to kill them.
Overall this type of character doesn't scale well into lategame, because besides +skills and max mana (capped at 35k which isnt hard to get, just bunch of average eerie crafts and few % energy items). +skills also increase damage a bit but not much. I was able to get my mana sweep to avg 15k damage. Thats ok, but you can get other elemental skills even higher (not even counting pierce). By other elemental skills I mean comparable novas that hit once per cast, like apocalypse or stormcall.
There is one area where it shines, unformed land. They dont leech you mana, so you can spam mana sweep without dumping mana every cast. This might be the cheapest fast clearing character for this area.
It doesn't scale past certain point as I said. I've seen stormcaller chars that deal over 20k damage without counting lightning pierce.. and that is fully spammable skill without any penalties. Comparable nova. You can scale it furher with umo, better rolls, while with feedback skill you are basically stuck at capped damage.
This is an issue with sorc overall, having to use another skill to kill immunes, while stuff like stormcall goes through everything.
Even the alternate passive damage, like hive, has this annoying delay and not full screen coverage, unlike paladins voj (used to kill fire immunes for apoc pala).
I'm not saying it is bad thing that casters need two elements to play the game, but there are casters that don't, and then playing sorc feels bit underwhelming.
Oh and killing immunes via kill procs while beign poison sorc, doesn't quite work, there isn't good enough proc (yes even fire cannonade from jared stone doesn't clear well enough with good gear).