I also assume that the Koksan self-propelled artillery, which NK has, does not exist since there is no gun with the range to hit Seoul.
Anyway, since it is an obvious lie I am assuming that we will see a massive attack on Pyongyang any moment now. After all, the biggest ace North Korea has - its artillery - is a lie, right? That's why all the nations around it bend over backwards to placate the three fat oafs that have ruled North Korea ...a lie.
As for your last point - trading Seattle for Seoul. That's a real question, and the answer is simple. It's not even about trading one for the other. It's the simple fact that the best time to have stopped NK was decades ago, but because that wasn't done, the best time to stop NK is NOW. More time only makes their capabilities (even the ones some consider to be 'lies') to become more effective. It will cost lives, and may even cost Seoul to be honest (and yes, I am one of those who believe the 'lie' that NK can annihilate a good part of Seoul), but the fact is that if nothing is done NOW that in the FUTURE it will be the cities of Tokyo and Seattle that get used as basically city-wide hostages.
The choice is simple - lose big now, or lose bigger later.
Please identify the artillery with such range.
The actual distance from the DMZ to Seoul is 35 miles, not 30km.
https://skeptoid.com/blog/2013/03/11/why-north-korea-cant-flatten-seoul/