Except for... you know Chaoticag, South Korea would have one heck of a time even trying to take possible one of the most easily defensible countries in existence.
It kinda makes the advantage not so clear cut.
The point isn't to annex NK once a war starts, just remove their navy and their air force. Once they can't do anything offensive, they can't mount an offensive. Not to mention that the US is South Korea's allies, and all it'd take are a couple drones to ruin what war capabilities they have in North Korea.
Nooooo, the point once the war starts is to somehow try to stop all the fixed artillery that North Korea has from wiping out a good chunk of South Korea. Just because a lot of their tubes are world war two era doesn't mean they can't throw a very big, very explosive shell into the middle of Seoul. Which would involve striking through the DMZ, also known as the most heavily fortified border in the world.
Which would be very bloody. To say the least.
In any case, I really do wonder if the Korean War finishing is inevitable. I mean, if all this posturing doesn't lead to it, what happens when the North Korean regime gets down to it's death throes? Moreover, am I gonna be sitting Camp Casey when it goes down, or will I be heading there as quickly as possible?