That's right. If you win 2 / lose 1, then on average 3 games are a net positive or +15LP. You do the math. And it takes even more to demote if you're at 33% since you don't demote as soon as you reach 0LP. The way ranking stall either way is way overdone and climbing / falling faster would solve most issues with current soloQ.
You could argue that someone with such a winrate would earn more LP than what he loses, but the reality is that it's simply not true for older accounts. Truth is the current MMR / rank inertia is way too huge to take account of a player's ups and down. If it takes so long for a player that dominant in its league, what can it be for someone that's just a bit above his league ? 17 games should be what it takes to someone with 66% w/r to climb an entire league.
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