There's a difference between "poor design" and "difficult to adopt", and I think confounding the two doesn't make sense. For another example, Python 3 has much

There's a difference between "poor design" and "difficult to adopt", and I think confounding the two doesn't make sense. For another example, Python 3 has much better design than Python 2, and the difficult adoption a result of having people fix what they had written using the poor Python 2 design, and making it easier to adopt would have meant preserving the poor choices. I don't know enough about IPv4 vs IPv6 to make a judgment in this particular case, but I don't think your argument broadly in itself here follows.