The easiest firewall in the world is one that is set up to deny all traffic from all sources. Which is how any decent firewall is configured by default anyway.

I'm not saying that running a private network doesn't provide genuine security value, only that it drastically complicates your networking architecture for very little security benefit. Organizations can decide whether that trade-off is worth it, for organizations with deep threat models like militaries and banks, it's probably worth it. For 99% of the private sector, it's folly.

"Private networking" as defined by assigning private-range IP addresses are only private as long as there is no route to your network, or as long as it's isolated on a dedicated vlan (even then, there could be some rogue machines).

In the first case, you need a firewall for IPv4 anyway. In the second case, that would also work with IPv6.

Disclaimer: I know nothing about Azure/AWS internals.

This phrasing is really problematic. Using internet addressing (vs ambiguous addresses) does not make your network "public". Just like using unique MAC addresses doesn't. Confusing global addressing with public reachabiliy is exactly the rhetoric used by AWS, Azure etc to scare people into building mazes of ambiguously addressed 10.x networks.

Therefore job security of old school network administrators is the main factor against IPv6 coverage.

Hopefully one of the big cloud providers figures it is in their best interest to have a much bigger address space and make all this busywork sinecure obsolete.

How is managing a NAT easier than managing a firewall?

This is a bit like saying “customers can barely manage driving a stick shift with a manual choke — we shouldn’t let them drive automatics!”

IPv6 isn’t amazing, but it makes many of these problems simply disappear. Of course [0] networks should be isolated, but this should be achieved with a firewall that, by default, disallows connections between the public Internet and private networks. And that’s about it — every VM has a globally unique address, routing just works, one company (if permitted) can connect to another company’s endpoints, firewalls can be deployed where they make sense instead of being forced to exist exactly where inconsistently-addressed networks meet, etc.

The entire mess of designing and negotiating allocation of extremely limited IPv4 addresses for private systems simply disappears!

[0] Beyond corp has something to say about this.