You're aware that matchmaking uses MMR to determine groups, not rank right? A D5 might have shit MMR and a P5 can have good MMR and they'll be pretty close.
HOW DO I KEEP ENDING UP IN GAMES WITH PLAYERS WHOSE SKILL LEVEL DIFFERS GREATLY FROM MY OWN?
There are a few factors that can make a match feel more imbalanced than it actually is. A teammate may have just had a bad game and performed worse than they usually do. Alternatively, as we’ve seen in LCS, snowballing can still occur despite the two teams being very evenly matched. Snowballing can then lead to the very reasonable perception that a mismatch occurred. Finally, both the Dunning-Kruger and negativity bias also play a role here in shaping players’ impressions of their matchmaking experiences overall.
For the matchmaker itself, the conditions often cited for mismatch are low concurrent users (CCU) or having a very high MMR. But when we take a deeper look at this pool of games, the impact on the quality of matches ends up being very, very low. Instead, the matchmaker is much more likely to increase the queue time as can be seen in the longer queue times seen in the Challenger Tier.
That is not to say that our matchmaker is absolutely perfect. We are also constantly monitoring our matchmaker and making any necessary tweaks to help reduce the chance that players of vastly different skill levels are matched together.