Also v6 did a bunch of things right. NDP and link local addresses for v6 actually work. The fragmentation changes were 100% the right thing to do. v6 extensions like SR and uSID are both solid and consolidate a lot of stupid stuff into something clean.
v6 had a bad, rocky start. A lot of that was completely inadequate attention to the transition, and the vendors fucked up almost everything for years, on their own gear and interop, but at this point v6 is fine.
Would I launch a v6 only service? No, because at this point the SPs are the problem. Verizon as of a few years ago and maybe now still didn't do v6 to any of their home users. So many things like that.