This is very valuable, but not sure if you think it contradicts my comment.

I'm not saying that IPv6 is incompetent, or that IPv6 implementations break backward compatibility, or that the problem can be solved without breaking bc.

I'm saying that while IPv6 breaks bc itself, dual stack does not, and even full migrations can maintain bc or gracefully degraded.

In essence, not all implementations IPv6 are good, and not all migrations from IPv4 are responsible, if someone is blindly team IPv6 or blindly team IPv4 in general there's a lack of nuance.