Unfortunately, this is a subject that I cannot discuss in detail.
Just consider that the direct effects of artillery would be only a small part of the effects on Seoul. A city that size deprived of power, water, and food would be a disaster management nightmare.
You are correct that the SRBMs are potentially a greater threat than conventional long range artillery. This is partially because of the wide variety of WMD payloads that could be delivered. How much destruction Seoul would receive depends on how those SRBMs are allocated between military targets and civilian targets. Traditional military planning would assume that most of those would be used against ROK and US military targets which are beyond the range of NK artillery. That assumes that NK actually thinks they can win a conventional war. I would be more inclined to assume that NK would inflict as much damage against civilian targets as possible to force an agreement that would ensure that survival of KJI and his regime.
Perfectly understand not being able to discuss this as I am sure it involves plenty of classified information not available open source.
I guess my point was that it is not a foregone conclusion that Seoul would look like Dresden after a NORK attack. 200-400 tubes even if only firing for a couple hours would make a mess of Seoul and knock out alot of civilian infrastructure to bring the city to its knees, but it could recover. But if 10,000 tubes were firing issues like power grid failure, water and food supply interruptions would be moot becuase there wouldn’t be any buildings standing nor many inhabitants left alive to complain.
Granted, the Dresden option does come into play if the NORKs can make a push south of the DMZ or if Kim can manage to strap a crude nuke on an A2 . . .
+1 on the inclination that Kim would focus his targeting on civies