Also important is the "priority speaker" function which let's a certain group, or channel automatically be louder than local chatter. So you can have a small subgroup actively coordinating and the fleet commander can give orders which don't get lost.

Mumble also has much better security/permissions. Last time I looked it was pretty easy to dump the list of active users on a discord "chat". That means you could always know if someone was forming for an attack etc.