Given that the error resulted from the STUN and ICE servers, which from my understanding exist solely to play a part in the NAT punching process, would this entire situation have been mitigated if things were end-to-end IPV6?
Only in theory. In practice even when IPv6 is in use, people have stateful firewalls that will drop unsolicited connection attempts.
Compared to ipv4 where there is UPnP and NAT-PMP with widespread support in routers, there are protocols to allow clients to reconfigure the router with ephemeral firewall rules, but they are not wide-spread and support is very spotty.
So in practice, users with just IPv6 would have the exact same problems and would be even more likely to depend on STUN and ICE because their firewalls likely won’t support client-side hole-punching correctly
