Three years ago, a user (not me) created a feature request on the old Discord forums:
(Screenshot on Aug 30, 2017. It got more upvotes after that as long as I remember)
I DO agree with this.
I know the new forums have similar requests like this, this and this, but they seem focusing on manual tweaks. Of cause allowing manual panning would also be great, but, in the first place, all participants should be panned apart automatically (meaning by default) on the start of a voice chat and when someone is coming/leaving while that.