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.
I think the reason this is happening is that the IPv6 infrastructure on most ISPs here was built for mobile phones. The few customers who are asking for IPv6 are just added to what was built for the phones which has completely different goals and requirements. Very few people run servers on their phones, do P2P connections or similar.
They said that v6 for home networks was frustrating, but it's not. The frustration is coming from the terrible v4 CGNAT, and that has nothing to do with v6 and everything to do with v4 being insufficient.
It's amazing how hard people will misattribute blame to v6 for the very problems it fixes.
