Ever since the new runes ive been match against full teams of diamonds and masters

Have they actually been diamonts and masters though? Because i was matched with a PlatV last night who played horribly. I checked his op.gg and in seasons 5 and 6 he was a Bronze. Thats an awefully high rank to achieve from being a Bronze.

Lots of High Elo players play normals during this time. Most have very low MMR in normals cause they don't play often, not much can really be done about that.