UPNP doesn't "punch holes in NAT." It is dynamically configuring NAT to provide a specific translation. The same kind of dynamic translation happens the other way for any allowed outgoing traffic, and lots of old NAT traversal tricks made use of that before UPNP was a thing.

The hole was always there. People get this topic confused all the time because the majority of network devices doing NAT are also acting as firewalls of varying efficacy. There are basically no non-firewall routers anymore, they all have at least simple network address ACLs.

The purpose of upnp is touchless configuration. If you care about security, that is orthogonal to your goals, and so it must be restricted by some other policy enforcement.