All three of those things have gotten better over the years, and I have little doubt that given the attention and effort that RedHat and Debian package managers get, portage could be a clear winner. But the portage we have now has too many pitfalls to be the best all-around choice.
Portage is not used.
The broadness of the system isn't quite as vast as many distributions but running a desktop / dev workstation I have never encountered a package not available that I needed.
Exherbo may not be for you. It values users who are willing to be developers as well, and augment the system with the packages they need. You want others to do the work for you, that's not what Exherbo is about.
Besides, the original discussion concerned what package management system was best, not if it had tool X, Y or Z that you claim is very often needed.
If you can't be honest about its shortcomings, you won't be able to convince anyone to try out your pet project. It doesn't matter how reliable and trouble-free it is at managing the core of the system if it immediately degrades to "build it yourself" anytime you want to use something that's not popular enough to make the cut for a live CD.
I like to think my comments were honest: I admitted that the system while technically superior does not have the breadth that larger distributions do, but that for my purposes it was sufficient. You ignored that and found some packages not currently packaged in an attempt to disprove my experiences. Furthermore I admitted that the project may not be for you since you expect different things from a distribution than many of us do. What is dishonest about any of this? I have been incredibly frank.
Besides, one of the nice things about Exherbo is that it handles the nonexistence of a package rather seamlessly. You can compile it by hand, install to a tempdir, and then have the package manager merge it directly while giving you the ability to specify information about the package (metadata, dependencies, etc.). And then of course the package manager can uninstall it when you no longer want it. This makes the problem of "build it yourself" kinda moot.
I'm not going to bother responding to the "make the cut for a live CD" remark since obviously the there are far more packages than would fit on a liveCD or liveDVD.
It has many of the strengths of Portage, and even go beyond (it builds from source, and users may configure package dependencies, like USE flags on steroids -- its declarative language used to write packages is also used to configure them, so you can do more than just passing flags to a package). But it offers a substantial advantage, because builds are deterministic. The set of installed software (with all needed configuration) is determined from a config file (or many), and from this it's always possible build the same system.
This means that upgrading always end up in the same state as installing from scratch. This also mean that common packages can be cached as binaries, without risk of breakage - it only downloads a binary package when building from source would build exactly the same binary.
Nix also feature atomic upgrades and rollbacks: it only touches the running environment as the very last step of the upgrade (setting up a symlink), and stores the previous versions of packages until garbage collected, so an upgrade stopped in the middle can't break your system (the exception here being kernel upgrades). Indeed, if you interrupt an upgrade or install at any stage, just issue the command again. (also, this architecture makes it incredibly concurrent)
NixOS is a distro that uses Nix. It can provide a GRUB menu to boot previous versions of the system. When you upgrade, you can have it affect running system or only upgrade after a reboot. Either way, when you reboot GRUB will give the option to also boot the system you was using before the upgrade. On a technical level, Nix works a bit like a git repository: each package is addressed by the hash of its derivation (that says how to build it, and all its dependencies), and if more than one system version uses the same package it gets stored only once.
Coupling NixOS with Nixops, a deployment tool; and Disnix, that does service-oriented deployments (like Docker), they can help build more repeatable systems for production servers too.
Some links:
http://lethalman.blogspot.com/2014/07/nix-pill-1-why-you-sho...
It's a series that walks you through setting up and using nix. It found it really simple and satisfying - I now use nix on Ubuntu.
I feel ashamed that for the last ten years I could not find a kind word to the portage developers. For what is worth, they don't care.
Paludis does correct dependency resolution while Portage just pretends to.