My point was not about the user being able to work around game limitations but to assert that this is, first, a game limitation, wherein it failed to account for the existence of NATs. NATs aren't some new problem: my computer has not had a public routable IP address essentially ever, as even when I was using dial-up in 1995 I had set up a Linux server in our basement to use NAT (as I wanted to have multiple machines in my house always connected). I just don't see why CGNAT is somehow bad or worse or even different than NAT, if the game supports NATs (which it sounds like in your case it doesn't).

Yes: "symmetric NAT" is useless, but I have not yet seen a CGNAT deployment use symmetric NAT. I would just go so far as to say "symmetric NAT is an example of a technology that is not and never will be good enough to be called carrier grade" ;P. So like, that NAT can and has sucked shouldn't be a demonstration that all NAT everywhere is entirely useless.

It could very well be that CGNAT deployments don't have support for PCP, (or the related NAT-PMP and UPnP mechanisms that it is a successor to), which would suck. I haven't checked this yet. However, if they do, you should be able to do just about anything you could on any private NAT setup: these protocols let you ask your NAT to open a reverse port mapping to your system on a routable IP address, and you can use them with external tooling (they don't require you to be inside the app listening on the port or anything).