[{quoted}](name=Ice Weasel X,realm=NA,application-id=A8FQeEA8,discussion-id=WJMhxma6,comment-id=0001,timestamp=2019-12-17T15:14:48.029+0000)
I think this is already how team MMR functions. It takes the average of the team and matches you against other teams of the same average. The difference is in perception since only your individual rank is displayed explicitly by Riot. MMR is unknown to us (3rd party MMR is extrapolated, but not exact).
It's not your rank that determines your team and opponents. It's your hidden MMR.
It is not the same thing...
If i play with you, then you and me will TOGETHER get ONE rank.
If i play with my friend Bob we will TOGETHER get one rank.
If i play LoL Solo/Duo ranked, then im stuck with the rank i get because there is no other chance... While if you could get several ranks depending on who you play with, then you "always" have am extra chance to do better with someone else.
If you dont understand this, then i suggest you try playing Star Craft 3 (it is free)