Solo mmr

you have a separate MMR per game mode.

a diamond player who never played normals, who goes to play his first normals game, will find himself placed in very low/neutral elo. "and up against a silver player"

if you primarily play aram and you lose because you get RNG screwed and only own champs like skarner and evelynn then you might find you have a better shot in normals with fair games and you'll play against better opponents.