In my experience it displaced Mumble and Teamspeak only for casual gaming. If your group is strict enough about muting/kicking people who refuse to fix their mic settings, Mumble or Teamspeak is generally better -- better quality, local volume adjustments, less resource hungry, open mic not being the default, etc. Think tryhard esport players, or just people with old hardware (probably 90% of CSGO players )).
For my group this wasn't about mic settings but mumble being bad out of the box. Maybe because we didn't pay for the servers and used a free something, maybe because of bad luck, I don't know, but every experience we had with mumble was terrible. For teamspeak, while the voice part is great, the message part is (or was at least in ~2016) lacking compared to discord. We were coming from skype/twitter which had better support for """rich messages""".
I think they displaced Skype, mumble and teamspeak too.