That's my thought too, Mumble's text chat is terribad, the UI looks like crap. The onboarding is typical of non-hipster F/OSS. The setup guide for servers isn't "run murmur.exe", it's "run openssl commands to generate a private key and generate a CSR" and the setup guide for clients is "if you lose your client certificates, you potentially lose all ability to connect, and permissions/rights, hope there's another admin".
Also, the access tokens option seems absurd from a UX perspective. Instead of just asking for a password with a remember box, you go to Server > Access Tokens and paste a string in and it'll attempt it the next time you're prompted for a passworded channel or server. Small things like that.
But it has the absolute lowest latency I've ever seen for VOIP, beats Discord significantly in quality, latency, and security (mTLS auth, client certs, pin your own CA for server, you control TLS on both ends). From a strictly engineering POV it's excellent. It also has some pretty amazing features for voice control, passing audio downstream/upstream into parent/child channels (eve players might get what I mean for fleet ops).
TeamSpeak tries to do too much, with chat, filesharing, and now no one really wants to host TS3 other than it being concentrated on a specific few like OVH because half of TS's server services can be misused for reflection spoofed DDoS attacks.
I'm not sure what Ventrilo is these days. They would not sell you a personal use licence at all - you had to sign up to "resell" a minimum of several thousand slots, and increase your purchase every contract period, or they would terminate all of your licences. You aren't permitted to run a community, nonprofit server for yourself, and at $1-2/slot/month a large community server would never happen for cost reasons.