Both examples benefit much more from simply spamming Holy until kingdom come.
The wasps/ bees don't cast their Final Sting until they're about to die, which means that even regular aoe is often enough to kill them before the cast goes through but quickly doing a single target skill on them works just as fine.
Holding a potent aoe until they cast it to then stun them is a gigantic loss over aoeing as usual and simply doing 1-2 single target skills when they're about to die.
And as for Twinning mobs: they hit harder but the wall to wall was easy enough to heal without anyone stunning/ interrupting at all when they came out.
Did the tank need some extra healing if both had their buff up? Yes.
Was it worth holding Holy to interrupt instead? Absolutely not, not in this universe and not in any other either.
In most parties I've been in when those dungeons came out, neither the tank nor phys ranged stunned/ interrupted either cast. It wasn't designed to need that, it's simply a little bonus if it does happen.
All three healers could heal through it just fine unless the tank also didn't use mitigation. Then it got spicy. Also, in worst case invulns exist... unless you're DRK, of course c:
So both examples are not examples of it being beneficion, only of "it theoretically could be used later but it's not a good choice... you could, but please don't".