I know I am not your favorite poster but FFS this is why I keep trying to get attention to the issues made by using Ranks for Duo restrictions and Not MMR.
The Enemy has 2 sets of duos on it.
Look up the Voli and Teemo on the enemy team.
My basic assumption is Riot has ranks as a Class interval. If they used the old values from Season 2 (70 points per division) then its a bit more then 1 class interval assuming equivalent point value, arbitrary systems so that's not a guaranteed correct assumption. So we don't know Riots internal Values but if you port this information into Elo's System expectations you see a 200 point or a 280 point Elo gap. Converted into win probability, The skill gap between the Teemo and Volibear Duo is going to be 76%to24% for 1C or 83% to 17% for 280 Elo.
Because MM builds teams to try and balance out MMR with who ever is online + some extra points splashed in for premades. That means it eather looks for similarly mismatched Duos, Or it grab's who ever is around and then There's 2 ways to balance this. Use a bunch of folks in-between the two who are closer collectively as a team. Which would result in Leaving the teemo outmatched by everybody and the Volibear above average. Or it can try and find the a similar Gap of players which creates real RNG Lanes biased on matchups with folks getting stomped or stomping if they don't vs their equivalent, plus the weak link is not a duo so there's a synergy loss.
Riot knows the middle and lower end of the curve will have quality issues, so they aim for popularity. Look at how they set duoing up.
Iron Tier: Can only queue with Iron, Bronze, and Silver Tier players.
Bronze Tier: Can only queue with Iron, Bronze and Silver Tier players.
Silver Tier: Can only queue with Iron, Bronze, Silver, and Gold Tier players.
Gold Tier: Can only queue with Silver, Gold, and Platinum Tier players.
Platinum Tier: Can only queue with Gold players, Platinum players, or Diamond players who are at most two tiers above them (so Plat I can queue with Diamond IV and Diamond III, Plat II can queue with Plat I and Diamond IV, but Plat III can only queue up to Plat I).
Diamond: Can queue 2 divisions up or down (so Diamond IV can queue with Plat I, II, and Diamond II, III, etc.)
Master Tier: Can only queue with Master, Grandmaster, and Diamond I and II Tier players.
Grandmaster Tier: Can only queue with Diamond I, Master, Grandmaster, and Challenger players.
Challenger Tier: Can only queue with Master, Grandmaster and Challenger Tier players
Competitive quality is restricted to smaller ranges only as you go up.
Wish folks would take the time to do some basic research on Elo and MMR. Its not that complicated and you can have a better idea of what Riot does or can do by learning the mathematics then randomly guessing from personal experience.