That's not true anymore.

IPv6 allows for more direct connections for services like VoIP or Tailscale, since UDP hole punching between two firewalled public IPv6 addresses usually just works, but doesn't between two clients both behind a "port-restricted cone" or "symmetric" NAT.

As a result, connections have to be relayed, which increases latency and is just outright infeasible for some non-profit services that don't have a budget for relaying everyone's traffic.

Anecdotally, I've also heard that you can get better routing via IPv6 on IPv4-via-NAT-only providers these days, as the provider's CG-NAT might be topologically farther away than the IPv6 server you're connecting to.