Original source can be found here.
History Lesson.
Let’s start our history lesson from the very beginning. Vault of Glass contains 2 main raid bosses: The Templar and Atheon. Each boss ascribes to their own special rule, which I will be naming after them. The Templar fight follows the titular Templar Rule, which holds that the boss is immune to or shielded from all forms of damage until players successfully engage with the boss’s mechanic. Only after completing the mechanic can players begin a DPS phase. This rule is can be applied to most raid bosses in D1 and D2, and it’s the only thing separating said raid bosses from your average strike bosses. The beauty of these fights is that they can all be one-phased, but still feel more engaging than your average strike boss by requiring the successful completion of their respective mechanics. Examples (with minimum requirements) include:
Templar (Vault of Glass; use the Relic to break its shield)
Crota (Crota’s End; DPS his shield and use the Sword to damage him)
Warpriest (King’s Fall; activate each plate in correct order)
Vosik (Wrath of the Machine; throw balls at his face and shoot monitors)
Aksis (Wrath of the Machine; kill color-coded Servitors and throw balls at his face)
Bathing Crystals (Leviathan; activate each plate)
Calus (Leviathan; kill skulls in the void realm)
Argos (Eater of Worlds; break shield using Vex craniums)
Val Ca’uor (Spire of Stars; destroy two ships and throw balls at his face)
Morgeth (Last Wish; acquire 10 Taken Strength stacks and get balls in your face)
The Atheon fight, however, follows a different rule. The Atheon Rule holds that the boss can be damaged at any point, but has an insane amount of health; however, players can acquire a damage-dealing buff by properly engaging with the boss’s mechanics. The Atheon Rule is very similar to the Templar Rule, with the exception that it opens up the possibility for extremely coordinated and highly-leveled teams to bypass the boss’s mechanics. The bypassing of Atheon-like boss mechanics is typically not frowned upon, as doing so is a special challenge in its own right. Also, like Templar-style fights, Atheon-style fights can all be one-phased after successfully completing the mechanics. Examples include:
Atheon (Vault of Glass; escape the past/future for a buff)
Golgoroth (King’s Fall; stand in goo pit for buff) [how could I forget you?]
Garden Dogs (Leviathan; empower spores for a stacking buff)
King’s Fall brought with it a 3rd type of boss fight, which follows the Oryx Rule. In the King’s Fall raid’s final fight, the Oryx Rule mandates that a specific amount of phases must occur in order to defeat a boss. In the case of Oryx himself, that means 4 phases of mechanics and DPS checks must occur in order to defeat the boss. Ergo, one-phasing is impossible, which in my opinion is lame, but that's a different topic altogether. Examples of Oryx Rule fights include:
Oryx (King’s Fall; survive 4 phases)
Shuro Chi (Last Wish; rush through 6 phases)
If you couldn’t tell already, every raid boss pre-Last Wish has been accounted for. Every prior raid boss adhered to either the Templar, Atheon, or Oryx rule, which all demanded strict adherence to the boss’s mechanics. All but 2 could be one-phased after mastery of the boss's respective mechanics. This, however, changed with the Last Wish raid’s first and final boss fights. Kalli and Riven both adhere to Strike boss rules. In other words, they are fully open to damage (and being one-phased, or technically 0-phased) whether or not the mechanics of their fights have been engaged. This has led to teams stacking up in corners and nuking Kalli without paying any attention to her symbols, plates, or safe rooms. It’s also led to the infamous Riven cheese, which in my eyes, is not a cheese, but a failure of the raid designers.
So what happened in Last Wish?
This brings us to Rule #1 of designing a raid boss encounter: bosses must hide DPS phases, even mere seconds of them, behind mechanics. Rule #1 has been achieved through the Templar, Atheon, and Oryx Rules for various different fights. First mechanics, then DPS. Every time. Kalli and Riven drastically changed that and placed DPS before mechanics, which has led to a very obvious outcome: people are skipping the mechanics. The solution is not to nerf Cluster Rockets. If a team of Edge Transits can “cheese” Riven, then it’s very obvious where the problem lies. The raid design team has unfortunately failed for both the Kalli and Riven fights.
The solution, however, is pretty simple (but probably not so simple to code). Kalli should adopt the Atheon rule — let her be prone to only minor damage while she’s booping people off plates, and let each cleansed plate add a stack of a damage dealing buff. With that change, if players are able to stack in a corner and kill her before engaging with the mechanics, it at least will not be so trivial.
For Riven, the most obvious solution would be to have her follow the Templar Rule and switch up the eye-shooting mechanic. Rather than having a DPS phase followed by shooting the eyes, have Riven be immune to all damage until her correct eyes are shot. Shooting the wrong eyes will cause a wipe, whereas shooting the correct eyes will apply a damage dealing buff and open Riven up to a 10 second damage phase. With that simple tweak in mechanic ordering, the Riven fight can no longer be easily cheesed. Players will need to at least bait, call out the eyes, and then perhaps be able to one-phase her with 3 to 5 players.
Too Long; Didn't Read.
The Riven "cheese" is a fault in basic raid boss design and should be a lesson for future bosses. If you give players a DPS phase before mechanics, they will obviously always ignore the mechanics (give them an inch, and they'll take a mile). Adhering to the Templar, Atheon, or Oryx Rules avoids this issue.