I used to hang around the Github repos of zypp and zypper while building zypperoni, got to interact with the devs a bit. For instance, async installation is never happening in zypper as RPM doesn’t support it and there are no plans to support it. The somewhat faster way of installing packages using RPM single transaction has weird requirements that sees zypper trying to download all the packages in advance even if you’re doing just a dry run, and so on.
Deb is easier for end-users to unpack, modify, repack IME. There is a single package dpkg-deb to unpack and repack (as easy to use as xz). Once unpacked, the files/executables it installs and all the pre/post installation and removal scripts are neatly stored in its own separate folder/file. You just modify the file(s) you want and call dpkg-deb to repack the folder.
With RPM, you have to unpack, get the pre/post scripts separately, build your own specfile…
Also, rpm is slow compare do deb. Both dnf and zypper suffer due to this.
Though both have made strides to paper over these limitations in their own way.
At the very least, an extensible standard with mandatory standardized core components (like Wayland
Like minds think alike. 
I was thinking of Wayland (and pipewire) too when I wrote that comment. If it could largely replace the mess that is X11 in short order (sees initial release was in 2008 
), I don’t see why package managers can’t do the same.