The package format is almost irrelevant TBH. Most packages are not interoperable between distros due to the versions and names of dependencies. That is not something that gets fixed by a standard package format. Packages don’t even work well between different versions of the same distro. largely due to libc - anything that depends on that is built against a specific version and when you upgrade it you need to rebuild and install everything that depends on it. Similar problems exist for all compiled dependencies on a distro.
And while some packages of the same format can be installed on multiple distros (mostly those based of the same foundation) most cannot. This is what the newer package formats (like flatpack) are trying to solve - by including all dependencies inside the package.
So a standard format does not really solve those issues, so there is little advantage for one. At least not one of the old school formats. And the wars are not really over the format, they are over the tooling required for that format. At the end of the day RPMs, DEBs, and arch packages are just tarballs of files and some meta data (and there is even a tool that can convert between them - though anything with dependencies quickly becomes a complete mess). It is the build and install tooling that makes all the difference.