> 1) my stateful firewall is going to break most of that anyway
Stateful firewalls and even regular NAT aren't much of an issue for P2P, but CGNAT is much more problematic [0].
> 2) if cg nat is as popular as people claim then they won’t be doing that as it’s not an edge case
You'd hope, but people tend to be pretty slow to update their networking assumptions, so this is still pretty common. And it doesn't help that most CGNAT users tend to be either from poorer, since poorer countries and mobile data providers are far more likely to use CGNAT than legacy North American ISPs.
> people tend to be pretty slow to update their networking assumptions, so this is still pretty common.
My ISP doesn't do CGNAT in FTTH deployments, but I'm paying extra for a static IPv4 allocation anyway since I was increasingly getting hit with captchas every time my IPv4 rotated to flagged IPs that were trashed by my fellow subscribers with poor infosec practices - i.e. 99.9% of residential subscribers.
Once I got a static allocation, captchas are getting easy to pass.