I believe the claim is that, IF IPv6 had been a much more minor modification of IPv4, including just a change to the packet structure to have a larger address f

I believe the claim is that, IF IPv6 had been a much more minor modification of IPv4, including just a change to the packet structure to have a larger address field, it would have seen more adoption more rapidly than the current version of IPv6 which also changes everything else about the L2-3 stack. Sure, you would have still needed new devices and that would have taken some years, but as long as the network architecture remained the same, it wouldn't have required a quarter century to get to 30% adoption. I don't know that I believe this claim at all, but it is at least coherent and possible (unlike claims that N-bit addresses could have been added to IPv4 in a backwards compatible manner). Perhaps SLAAC, the focus on routable end user devices etc were indeed major distractions that pulled focus away from a move to a new larger address space - which is the only thing people actually wanted from IPv6.