I have seen and been matched with too many 4 man groups and it's clear from my personal experience that I do not work well being matched with such groups. Particularly in normals I don't see where it would be that big of a problem to allow summoners to opt out of such situations where it really doesn't matter what they say, think, or do, it's never what the group wants and is quite frustrating experience for everyone involved. I think it would be incredibly helpful if you allowed players the opportunity to decide if they want to be matched with 4 man premades.

tl:dr 4 man premade normals suck for all parties, please allow for solo players to opt out of such situations.