Port forwarding and hole punching have different objectives and outcomes, and I believe PCP only caters to the former.

While the outcomes might be similar (some inbound connections are possible), the scope (one specific external IP/port vs. everybody) and the semantics ("endorsement of public hosting" vs allowing P2P connections that are understood to require at least some third-party mediation) differ.

I also don't think that port forwarding is possible through multiple levels of firewalls (similar to "double NAT").