It is an advantage to have one package manager that works on any Pup (be they using upstream Debian, Ubuntu, Void, Slackware repos or whatever).
On the other hand, Debian and Ubuntu already have an almost perfectly reliable package manager that properly manages installation from their official repos.
PPM, and specially with pkg, tries very hard, but it is a re-invented wheel that is never going to be perfectly round...
Mixing package managers allows a kind of anarchy, and the freedom, like a breath of fresh air, is undoubtedly pleasant, and it is certainly true that the format of dotpets is very simple so they are both easy to understand and create and use. However, it is fair to say that the DebianDogs, for example, provide a simple-to-use GUI make deb utility (original version, somewhat modified, came from Puppy community I think?). Nevertheless, the internals of deb packages remains complicated, unlike the attractively simple tar.gz approach of dotpets. And official dpkg/apt does not work with Void Pups or Slackware Pups of course any way.
For my own main distro desktop I personally prefer to use reliable upstream distro package management (though it is painful to learn more than one), though I do occasionally supplement that with portable apps/sfs packages, and sometimes self-compiled, but stored in /usr/local/bin or /opt or ~/wherever, and in such a way that they don't mess with apt/dpkg installed files....
It is certainly difficult to avoid breaking a system when an anarchy of package managers is allowed - the mix is a nightmare, though fun and flexible, but the chance of breaking system can be high, though not if just using PPM/pkg for simple bash/gtkdialog type dotpets that don't mess with apt/dpkg installed files - so it depends - and obviously if installing libs then nightmare is inevitable and especially when /lib maybe now more likely to be /usr/lib... a problem for sfs addons too...
I think it is great that the Pup alternative, VoidPup, can use official xbps void package management or PPM/pkg instead if you so choose. The risk is left to yourself, but so is the resulting familiarity and fun, and disasters .
Trouble with Puppy just moving to using dpkg/apt for its Ubuntu/Debian variants is that it becomes difficult to justify using such Pups when DebianDogs exist, and especially when DDs by design also provide most Puppy utilities and more besides... and when installing debs, DD distros by default strip out lots of docs and so on to keep the resulting installation similarly small too (though on the whole disk storage size is irrelevant, but small root filesystems do remain useful for running whole distro from RAM or in small virtual machines).
My own feeling is that Puppy is best to remain a system that encourages anarchy (and accept that 'can' also mean 'breakage' at times); that's what Puppy is. Yes, it is a great development that new Puppy can use official package managers (and a sensible development, I'd say, ever since Puppy moved to relying on upstream repos) for those who rely on Puppy as their main Linux system. However PPM is a bit rusty and I thought pkg (using PPM partly?) is the future of Puppy anarchy in terms of universal Puppy Package management(?) So official upstream repo package managers should be an addition and not a replacement for PPM/pkg, or why bother using Puppy? I can understand a developer not wanting such a 'mess' though - but there are advantages to that crazy 'anything-goes' approach - especially on this wild forum, and especially if you enjoy the fun of that crazy lack of conservative management.