Not many firewalls support NPT. OpenBSD PF doesn't, where IPv6 NAT works much the same as IPv4 NAT.
I wouldn't put much stock into that article. Many of their points are IPv6 pros (and the sections seem to make that clear), and many of the cons simply boil down to IPv6 being different, often necessarily so--for example, PTR records for a 128-bit address space were always going to be long even if the delegation prefix chunks were larger (e.g. 8 or 16 bits instead of 4). And I don't see how any of those problems constitute a nightmare.
The only real pain point for IPv6 deployment IME is DHCP.[1] DHCPv6 was never even supposed to be a thing; the very fact that it exists shows that the alternatives can be replaced or supplemented. But either way this problem really comes down to tooling and operating system support. IPv6 deployment and the standards and software for deploying it will mature together, and complexity will ebb and flow as alternatives enter and leave the fray. It could never have been any other way. IPv4 was hardly without its hiccups. Heck, the switch to classless IPv4 addressing was somewhat bumpy and confusing even as late as the early 2000s simply because a lot of software, including standard tools like ifconfig(1), didn't make it ergonomic or even possible. Frankly the latent complexity is still annoying.
I think it pays to remember that a lot of these articles are written by people with an eye toward job recruiting, interviewing, and generally grooming their credentials. The conclusions don't matter, they're just an excuse to exhibit familiarity with the technical details. They're a sales pitch for the author, and that essay is a particularly good one--the author demonstrates a comprehensive familiarity with the issues, notwithstanding their framing and conclusions.
[1] The biggest pain point in earlier years was the need for BSD Sockets API support in application software. But it seems we're mostly over that hump, notwithstanding the regressions caused during the shift to cloud computing, where IPv6 support was and remains much more immature than in the wider ecosystem.