Seoul has 20 million people and its 35 miles from the DMZ.
13,000 artillery units including 170mm artillery batteries and 240mm rocket launchers.
Not to mention the chemical and bio weapons.
Oh and then theres the 1.2 million man army. Not the best equipped or trained but then they only have to go 35 miles.
I wouldn’t be too sure about the training. One time the “G” man mentioned that some South Korean guards caught some NK infiltrators swimming under water to infiltrate the South.
They killed them with hand grenades and recovered their bodies. He said every one was powerfully built and looked like they could have handled about anyone.