So it boils down to, as mentioned in your post, the more iterations there are then the more likely the better team will win, thus the Korean teams, being better, will more likely win the more iterations there are in a series. That seems like it's stating the obvious a bit, no? I like it, though, it's clear that work went into this.
The actual reason Korean teams are so hard to defeat is because they take part in what most people would consider completely absurd training regiments for the game. 8+ hours a day pretty much every single day on a single game is something most players would consider berserk. You don't see pretty much any other career with the same hours (most jobs let you have a day or 2 off every week), yet to stay competitive in top-tier eSports that's considered the norm. Add on the fact that in most Western countries, playing games for that long isn't the most socially acceptable thing out there (partly because it's not very sustainable unless you're one of the top players in the world and can routinely bring in tournament money, making it not look like a 'real job') while in Korea it's not considered nearly as bad means they get more support for choosing to pursue gaming as their livelihood in the first place, and they typically have more easily accessible local tournaments to try and win money to live on anyway, as opposed to many Americans having to drive 3+ hours for the nearest tournament unless they already live in a big city.
Koreans have a lot of things going for them in terms of why they typically win eSports in games they actually play, and a lot of it comes down to the fact it's more socially acceptable there and the fact they're willing to go through what other people would consider crazy training that would burn out most other people on the game.