TL;DR: Matchmaking has a couple of quirks that amplify the harmful impact of smurfing, even at high ranks like diamond. This situation creates a knock-on effect that makes matchmaking worse in all ranks.

Tracker.gg has recently started showing party composition of teams. This feature makes it a lot easier to understand how the game matches parties against one another.

I thought, and hoped, that the game never matched 5 stacks against 5 soloq players. Sadly, turns out this is not the case. Here is the latest example that I've stumbled upon: exhibit 1.

Surely the game tries to match teams with similar party compositions against one another, and it does that for the most part. I believe anomalies like exhibit 1 happen because of another quirk in matchmaking: The game uses MMR to match you against players, but party restrictions are implemented through visual ranks.

The quirk above opens up the game to more abuse. It actually makes smurfing more profitable. If you smurf, your MMR will usually be higher than your visual rank. If your MMR reaches high diamond while your rank is still in plat, you'll still be able to 5 stack, but the game will struggle to find another 5 stack of the same MMR/rank composition. Remember, a legit (non-smurf) diamond 3 player cannot 5 stack at all.

The outcome? The game matches the smurfing 5 stack against 5 soloq players, making the match even more lopsided in favor of the stack. This outcome has an even more insidious side effect: Legit players get punished more harshly for performing poorly against players at a lower rank. They derank, and become smurfs of their own in the lower ranks. This vicious cycle continues and matchmaking as a whole becomes painful for every non-stacking player at every rank.

This is yet another reason to tighten access to ranked and make smurfing harder. A 5 stack of smurfs on fresh accounts can get 10 unranked wins in one sitting, as people tend to forfeit a lot in unranked. It's laughably easy to make a smurf in Valorant right now.

(Side note: I don't think the Reyna on the enemy team in my example is smurfing, but her visual rank is much lower than MMR because she hasn't played that many games in episode 3. My point still stands though, as smurfs typically have the same MMR/rank disparity.)

Edit: Another example from the same smurfing squad, with even more egregious matchmaking. Why is there a gold in a diamond lobby?

Exhibit 2