At the moment, the Unshakable/Defiant system for champion and boss enemies does little but discourage players to try to use crowd control. I don’t think that’s the intention, and it sharply limits players’ options for dealing with difficult enemies in a group situation. It doesn’t help that in many cases, players use skills with built-in control effects just for their damage, triggering Defiant without actually getting the benefit of a well-timed stun or interrupt.
So here’s my suggestion for a clearer Defiant system:
Make Defiant a boon that can’t be removed and has a set duration. Instead of champion and boss enemies gaining stacks of Defiant based on how many players are nearby every time they’re hit with crowd control, have them gain a single “instance” of Defiant that lasts for a certain number of seconds. During this time, the enemy can’t be affected by hard crowd control effects like Daze or Stun. The length of time this Defiant effect lasts should not scale depending on how many players are in the area, but can instead be raised or lowered individually for each enemy to reflect how difficult that specific enemy should be to control.
To put this another way: treat Defiant just like Stability, only it is triggered automatically and can’t be removed by standard boon removal skills.
This would also open the door to a potential new condition:
Disheartened. Skills that apply Disheartened are rare and have long cooldowns. Disheartened removes Defiant from an enemy and prevents the target from gaining any boons (including Defiant) for its duration. Once Disheartened wears off, champion and boss targets become Defiant even if they weren’t crowd controlled during Disheartened’s duration.
Whether or not a system like this were to be implemented, I do have one more request: make Defiant more visible on enemies. For example, instead of having it appear among all of the enemy’s boons and conditions, make Defiant a larger icon to the side of the enemy’s health bar and/or next to the enemy’s nameplate, with either its duration or its number of stacks clearly visible to everyone who has the enemy targeted. That way it’s easier for groups who aren’t using voice chat to coordinate when they should use their stuns and interrupts, because whether the target is vulnerable or not is clearly visible.