The matchmaking fix last Friday was effective in most regions, but we're still working on more improvements for EUW where it didn't fully resolve the issue.
@SKAquaman Different regions have different population size and player patterns (eg in some regions, the top of the ladder players play more on mains, where other regions they play less). These factors make it so the optimal matchmaking tuning is different.
10.15 Patch Preview.
Starting to shape the worlds meta and focusing on counterplay for Aphelios/Yuumi. Full changes should be ready tomorrow. http://pbs.twimg.com/media/Ec1O3HnUMAA3Jku.jpg