If two players cannot queue together in Solo Q, they should NOT BE MATCHED IN A GAME.
Bronze Tier: Can only queue with Bronze and Silver Tier players. Silver Tier: Can only queue with 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 and Platinum players, with exceptions listed below. Diamond V: Can only queue with Platinum I, II, III, and Diamond II, III, IV, V Tier players. Diamond IV: Can only queue with Platinum I, II, and Diamond I, II, III, IV, V players. Diamond III: Can only queue with Platinum I, Diamond I, II, III, IV, V, and Master Tier players. Diamond II: Can only queue with Diamond I, II, III, IV, V and Master Tier players. Diamond I: Can only queue with Diamond I, II, III, IV and Master Tier players. Master and Challenger Tier: Can only queue with Master, Challenger, and Diamond I, II, and III Tier players.
Why can matchmaking override this? There is no reason that you shouldn't be able to queue outside of these limitations if matchmaking will put them together/against each other anyway. Like what is that? Just had a Diamond and Gold in the same ranked game. lol.