yarn npm publish would call internally yarn pack. So this would be a win. Unfortuately, it doesn't support the same CLI arguments then npm publish. Therefore first yarn pack is called to create a package.tgz per package, and with npm publish package.tgz this package is taken to publish to npm. Therefore, npm isn't responsible anymore to build the package. It only takes the tarball archive and publishes it.

I don't really follow this. If yarn npm publish already runs yarn pack, why do you want to run npm publish separately? You say that "it doesn't support the same CLI arguments then npm publish", but as far as I can see you don't supply any other arguments other than the .tgz file, which I would think wouldn't be needed at all if you just used yarn npm publish?
What I'm saying is, isn't yarn pack && npm publish ./package.tgz --tolerate-republish --tag ${tag} the exact same thing as yarn npm publish --tolerate-republish --tag ${tag}?