I do actually remember following its development, hate NAT, and of course feel constrained by the V4 32-bit address space. But V6 has its designs problems too and while over the years I’ve tried to use it, it has never been worth the hassle and, yes, is slower (probably because most connections are to V4-only sites).
Then we stopped sending html to insert into the DOM, and started sending JSON with a bunch of extra steps in between.
The fastest sites I see these days usually just reload the whole page pretty often.