Seriously, normal draft matchmaking is pure trash
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So right now, there are two MMR values for Summoners' Rift, one unranked and one ranked. However this means that even a fresh level 30 account has the possibility to get in a match versus a challenger who hasn't played normals that season (or kept it around 1200 elo).
My suggestion: Have both ranked and normal games modify the unranked MMR. That way those two would be close most of the time, which is much wanted. It ensures that high elo players get a decent practice experience without having the possibility to stomp noobs.