Comment by Xirdus

IPv4 stopped working fine some 30 years ago. The invention of NAT was caused by IPv4 not working fine (RFC 1631 was written under assumption it's a temporary solution). Hole punching is a thing solely because IPv4 stopped working fine. Much like Y2K, the reason IPv4 appears to work fine is because absolutely massive engineering effort was put to work around the parts that don't work fine.