On 17 Apr 2020, Michiel van der Vlist said the following...
 Mv> Can you expand on that? What exactly was a step backward and how and why?

IPv6 was designed in a way, that you can multihome the PAv6 allocation you
get from your ISP, so there was no need for PIv6 really.

So, it was initially not implemented, to keep the routing table small. The
IPv4 routing table is a beast these days. With fragmentation and people
buying /24 blocks left right and center, a full IPv4 routing table is now
nearly 800k entries .. and that's with filtering routes  * Origin: The Alien Mindbenders BBS (2:263/5)