From what I can tell, it's a lot better than that.
The Artillery option is not "reduce the biggest town in this half of the province to rubble" You want Plan Arsonist or Plan Dragon for that.
Artillery mounted on the walls will target anything flagged for destruction, which would involve runners and riders for the most part, so they won't really be mowing down civilians so much as demolishing key structures. Its only really practical to call down artillery for any structure that'd take more than half an hour to breach.
Barring wizards casting petty spells to create targeting beacons anyway. Kind of wasting the wizard unless they're just journeymen though.
Anyway for the butcher bills:
-Knight Charge
--Army Risk: Medium
--Elites Risk: High
--Assets needed for castle at risk: Knights(minor)
--Civilians at risk: Low
--Primary problem: Undead forces are less vulnerable to morale shock of a charge(which is like half the reason a charge works).
--Secondary problem: Necromancers free to cycle in fresh undead indefinitely.
--Tertiary problem: We JUST bloody tried that. Surprise, charges don't work so hot in urban environs.
-Wizard Push
--Army Risk: Medium
--Elites Risk: Medium
--Assets needed for castle at risk: Wizards(critical)
--Civilians at risk: Low
--Primary problem: Fronting wizards on the strategy means higher risks of spell backlash, when disrupted i.e. risking the Amethyst Patriarch.
--Secondary problem: Necromancers, if any, remain hidden, countermagic will come as a surprise.
-Defeat In Detail
--Army Risk: High
--Elites Risk: Low
--Assets needed for castle at risk: None
--Civilians at risk: Low
--Primary problem: Our army morale is low due to death of ruler, undead are natural morale threats and street fighting is historically extremely unpleasant for line troops. There is a high risk of the army breaking in a street battle
--Secondary problem: Strategy is vulnerable to flanking. We hadn't seen any enemy elites yet, but this strategy deliberately maximizes the surface area of our army, so if elites do show up they can snip off entire segments of the army.
-No Innocents
--Army Risk: Medium
--Elites Risk: Low
--Assets needed for castle at risk: None
--Civilians at risk: High
--Primary problem: We'd be butchering masses of civilians in the largest town in Sylvania. The streets will run so red with blood you could mistake it for a Khornate sacrifice.
--Secondary problem: The area is saturated with Dhar. It would not take much at all for necromancers to cast mass animate dead spells if they are capable of that while we're advancing.
--Tertiary problem: I'm not sure how much use the town is as a forward base after this. This is practically textbook "how you get a vengeful mass of wailing spirits".
-Artillery Is King
--Army Risk: Medium
--Elites Risk: Low
--Assets needed for castle at risk: None
--Civilians at risk: Medium
--Primary problem: The most important administrative structures will be likely destroyed by the process, which makes Sylvania harder to reclaim owing to the need to reconstruct maps, surveys and census records.
--Secondary problem: Reducing the most secure structures of the region into rubble reduces the town's capacity to serve as a forward base, though the dwarf contingent mitigates that.
--Tertiary problem: We'd find it hard to confirm kills on the necromancers and/or vampires if any.
-Fuego
--Army Risk: None
--Elites Risk: None
--Assets needed for castle at risk: None
--Civilians at risk: Total
--Primary problem: The part where we burn the whole town alive and have troops pushing anyone coming out back into the flames.
--Secondary problem: The town's value as a forward base is gone. A fire like that makes it no better than building a large field palisade for basing use. All records would be gone too.
--Tertiary problem: The smoke of the fire will be visible from Castle Drakenhof. Any remaining element of surprise is gone.
-Pyrofuego
--Army Risk: None
--Elites Risk: None
--Assets needed for castle at risk: Deathfang
--Civilians at risk: Total
--Primary problem: The part where we burn the whole town alive and have troops pushing anyone coming out back into the flames.
--Secondary problem: The town's value as a forward base is gone. A fire like that makes it no better than building a large field palisade for basing use. All records would be gone too.
--Tertiary problem: The smoke of the fire will be visible from Castle Drakenhof. Any remaining element of surprise is gone.
At least, that's my take.
