Is it? There are many benefits in principle to IPv6, but if my ISP continues to assign me a single dynamic IP, those benefits are entirely moot for me.
Your ISP assigns you a single dynamic /128? Which ISP is that?
Is the argument that there are no benefits to IPv6 for anyone/society because your specific ISP messes it up?
Right, but just because you don't happen to have IPv6 right now, how does that remove the benefits for others to have IPv6? That's like saying having a faster CPU wouldn't mean faster performance, because I don't have that CPU yet.
If your ISP is assigning you a single IPv6 address, they are doing IPv6 wrong. You should be getting your own /56.