they have separate mmrs, but they should most definitely be tethered, like they are in most games, including other mobas. there are entirely too many games in norms where it is 3-4 plats/diamonds vs all silver 2's or silver 3's. the only reason your norm mmr is that much lower than your ranked mmr is because you completely throw games in norms. another thing that should be done, again something that is done in many games besides league, is have a max spread on duos/trios/etc. a diamond player shouldn't be playing with a bronze player, plain and simple. i get we all have friends who we want to play with and what not, but you can do customs. most people have plenty on their friend list to do this. no point having a bronze in a mostly diamond game, or (what happens much more often), a solo diamond in a game vs all bronze.