Different MMR for Different Queues
What's the explanation for this? I'm sure Riot is aware that getting pubstomped by top-tier ranked players in Normals isn't very fun for anyone. So there must be a reason that you haven't implemented the simple solution of unifying MMR (or at least making Ranked MMR influence the others.) What is that reason?
The only thing I can think of is that high MMR players have longer queue times and you don't want them to have long queue times but... that's kind of awful if you're sacrificing everyone else's matchmaking quality for that. (Not that I particularly believe you are. I just can't think of any other reason.)
So yeah. An answer would be great. Maybe Riot gave one in the past and someone can point me to it? Maybe someone has better theories than me? I'm all ears. Or eyes.