I'd try nixpkgs before trying pkgsrc if for some reason I wasn't satisfied with ones that come with the distro. Not sure why BSDfying packages is desirable by itself.
One reason to try it might be that pkgsrc mostly solves the problems Nix solves with conflicts in a much simpler way, by allowing multiple co-existing branches installed to different prefixes.
Nothing against nixpkgs, but if the user is curious about how things are done in BSD perhaps he should try xbps before nixpkgs. It was written by a former NetBSD committer who wrote some useful programs for NetBSD's userland. I am biased perhaps but I believe it is faster than any other Linux package manager. Always looking for something faster so I am welcome to being proven wrong on that.
As a pkgsrc committer, xbps is nothing like pkgsrc. The underlying stuff is much more similar to something like Arch or Alpine Linux than anything that exists in the BSD world, and it's much less configurable than pkgsrc.
Actual package recipes. BSD-style packaging systems are written in BSD make using a mk/ framework rather than Arch-style shell scripts. If a package already exists for FreeBSD Ports I would check that first because it's much more similar to what I'm used to.
Fundamentally pkgsrc is built on very low level tools, awk, shell, make, cwrappers, and pkg_install, although you can manage it with high-level ones (obviously pkgin is there, but there's also a lot of other third-party tooling).
Why are you comparing pkgsrc to pacman. The orginal comparison suggested in the parent comment was between xbps and nixpkgs or other Linux package managers.
pkgsrc boostraps itself using a program called "boostrap" in the pkgsrc directory. It builds a version of NetBSD's GCC toolchain and has no reliance on the host's userland. IME, this is very reliable and is its single greatest strength. Beyond that, pkgsrc is only as good as the build processes chosen by the author(s) of the software being built. These of course vary widely in sanity and depending on the packages one is building the otherwsise sane pkgsrc build process can quickly become a black box with packages that pull in many dependencies. It does break sometimes, but this is a fault of the target software authors, not pkgsrc. pkgsrc is first and foremost a system for building packages.
Linux distributions OTOH tend to be much more focused on binary package managers. Most Linux users do not build packages from source. There is really no comparison.
Your comments do not sound like those of a daily NetBSD user. I have been one for the last 15 years and am therefore all too familiar /usr/share/mk. Most Linux users do not seem very comfortable with BSD makefiles.
The original commented suggested that XBPS was similar to pkgsrc. I suggested that XBPS has far more in common with Arch Linux's package manager than pkgsrc or anything else in the BSD world. As you yourself note in your next paragraph...
> Your comments do not sound like those of a daily NetBSD user.
I have commit access. Since three years ago. My name is on the latest release announcement.