Originally Posted by
Shurrikhan
This would depend entirely on mobs not progressing towards auto-attacks or future special attacks while stunned. If player behavior is anything to go by, they likely progress towards both. The stun would then merely delay readied auto-attacks from being cast, much like downtime does for us.
I.e., if one is stunned for 2 seconds with only 1.5 seconds left until auto-attack, they've lost .5s of autos; however, if they're stunned for 2 seconds and still had 2+ seconds left until their next auto-attack, their damage won't have decreased at all.
The same interaction would occur with special attacks, most noticeably the instant casts among them.
tl;dr:
Holy's total stun duration would need to have no gaps for it to provide even 7 seconds of complete damage mitigation (technically, still short of that, as any time until next auto eclipsed by the stun would not be affected).
On average, Holy likely instead tends to net about 3 seconds of trimmed autos from mobs being unable to use capped/readied auto-attacks, and briefly delayed castless specials, across the spam. Its utility value is both generally greatly overestimated and appears to come at cost elsewhere in the toolkit (in terms of bankability and modularity of free heals).