Your ranked MMR doesn't impact normal game MMR, ARAM, TT or Nexus Blitz queues.
They all have separate MMR.
To me, it's completely ludicrous that every time there's a feeling like you're getting unfair opponents or teammates, people try to pull the same Ranked SR statistics regardless of the mode/map in question, in order to provide evidence that Matchmaking doesn't work. There is no Ranked Nexus Blitz mode so anyone trying to make "this team is all Diamonds while my team is all Iron" argument, just doesn't work.
This argument would've been the same if you had a team of 5 professional basketball players going against 5 amateur basketball players on an ice rink challenge for the first time. What difference does their basketball experience make in ice skating? Absolutely none. And if you lost to these 5 basketball pros, would you really blame the organizer of the event that they had an unfair advantage, in a challenge that didn't even require of them to use their pro basketball skills in the first place?
Let me get back to my previous argument:
What's there to "skillfully" play in Nexus Blitz? It's a map completely different from SR, it has a completely different strategy, Baron and Dragons are gone, you have a jungle and a smite (you also double jungle so there's no X champ is just a terrible jungler), you can gank easily, you have arena matches, animated nexuses, some crazy buffs for winning/losing events... this experience is not SR experience. Therefore you can't compare SR ranked statistics in matchmaking over there to look for "more appropriate" teammates.
More "League practiced" players do pick up on mode nuances faster and understand the game mechanics better in a few tries (compared to a newer player) but you can't expect your exact carbon copy on the other side to make sure that both of you understand this new mode with the same speed and could reach the same conclusions in the same amount of time. There's more to player skill that reflects who they are and how they play League than with an MMR rating (their tier and division).
