I feel like this is one of the most frustrating parts of playing VDH in keys at the moment.
If Throw Glaive had an effect that prevented spell casting for like 2-3 seconds, or something like that, it would solve a lot of the grief with rounding up packs. Just talking pve here.
I think a 1 min CD on Chains will help a little next season but might miss the mark somewhat considering dungeon packs are often quite spread out and likely will be outside the range of chains in most cases.
Hopefully blizz can straighten this part of the gameplay out (among other things) for next season. It’s been a tough slog getting groups on the VDH this season and I feel like the rough time is only compounded by the frustrating mechanics of the spec.