Well, the other problem with Discord is that people have to opt-in to the groupings. Circles were publisher driven. If you were in my CS Friends circle, that was just where I categorized you. It was not akin to a FB group or a Discord server. In those, you have to accept some kind of invitation into the grouping, and you're made to communicate with everyone in the group/server. Circles were one way, from me to the circle. For a circle member to publish to all the same people they'd need to be connected to all of them directly in G+ and create an identical circle.

This is the same issue as group messaging in most instant message type systems (including SMS/MMS). It's forcing a full connection between all participants, when really we may only want a fan-out structure.

I haven't used it much (not as many people on it in my social circles) but WhatsApp's broadcast lists are like G+ circles in this regard.