I do agree with you on some points.
The system indeed ignores the GP, since there is the skill rating.
The system indeed designed to get everyone, eventually, to 50%. And that exactly my point. Based on that, a player with a positive win rate should theoretically climb and eventually get into K1, not matter how long it's gonna take. Positive win rate should make you climb. I have a positive win rate each season for at least a year and yet, instead of getting into K1 I'm finding myself struggling to stay at K2.
I'll try to find the statistics of the amount of players in each league to prove my point.