Why mix ranked and unranked systems?

Why mix Ranked and Unranked systems?
Why is it good that I’m currently at 4.3K mmr throwing 5K or 5K + mmr players at an opponent?
Why is this good?
Aside from the fact that he wins nothing with it, in return I fall on mmr, even if only a little but still mmr - and I don’t think that’s fair …

The whole point is to reduce the waiting time.