Mumble is a tool with its own strengths and weaknesses. It's not a social communication platform, so of course it sucks to run a community on it!
What it is is an excellent voice server. I've used it for intercom at a large live event and it was perfect. I've seen it used at a large LAN gaming event to successfully cut bandwidth usage almost in half. It also has broad support for positional audio in games - something that Discord notably completely lacks.
It's free, it's open, it's not bound to provider-operated servers, it has stellar latency and is very extendable. Please, find me another option.