Ha, yeah that sucks and I'd absolutely hate it if I were behind a CGNAT. But I believe most ISPs don't do that. None of mine ever have. Just like how most ISPs provide you with an ipv6 address range, but not all. Fact is that crappy ISPs can screw up your network no matter what ip spec you're using.

And I've never heard of a business network being behind an ISP controlled CGNAT. A NAT you control can be nice.