she initializes the dialog only if you come quite close to her. she only wipes your party if you basically run straight to edge of the fire, ignore the floating crazy fire witch, don't prepare with fire resistance and unlink your party to space out your group a bit so you don't get one shot.
i learned a proper setup before a boss from the lvl 18 troll who can also wipe your whole party with a single battlestomp.
you may call it foreknowledge, but seeing a crazy burning floating witch in a large fire area littered with corpses should tell you:
-warning dangerous
-she probably does fire damage
-take precautions in case you can't beat her straight away
Those are cheesy out of combat options to perform in dialogue, unless Larian intended it as a nod towards the infinite dialogue exploits in BG2 where you could initiate dialogue with Lichs and then kill them as they stood there expecting to have a conversation. I expect you were also an advocate for stealing Kangaxx's ring twice, since not many people seem to object to thieving their way to victory in Original Sin 2.
they are as cheesy as you want them to be. i don't find it particular immersion breaking that your other characters slightly shift away from the person who distracts her with dialogue.
the assumption that she will start with some hefty fire damage (burning witch floating through fire, quite above the area level, magister corpses) is basic observation, not cheese or arcane farsight.
/warning semi serious hyperbole
do you really want a game where a totally oblivious player walks his tightly spaced party into a heavily indicated powerful boss and still comes away with it?
i learned my lesson with one of the trolls and who thought me how dangerous bosses 5 levels above your party can be, maybe other players learn that lesson with the witch.
i only played through on tactician mode, but even then i always keep one character a screen away when the game tells me difficult fight ahead to recover from mistakes.
