That's why I said in the real world and not in theory. There are only a handful of ISPs I can pick from and they all have very broken IPv6 support due to bad CGNATs. Yes in theory it should work, but in practice on consumer grade internet you're better off using IPv4 only here.
If the CGNAT is bad, that's a problem with the CGNAT. If your ISP won't turn off CGNAT without turning off v6 at the same time, that's your ISP's fault.
v6 works completely fine in both cases. Your problems aren't with v6.
They're not claiming IPv6 is bad. They're claiming that they can get good service based on IPv4, or bad service based on IPv6. Of course it's the ISP's fault that the IPv6 service is bad, but, since ISPs usually hold local monopolies, overall it means that they are forced to use the IPv4 network - unless they're willing to move to a different area where there are ISPs offering good IPv6 service as well.
