> Ubuntu is nothing more than the Debian "unstable" branch with Canonical branding plus non-free packages.
This just isn't true. Ubuntu is typically quicker to update popular packages, such as desktop environments, kernel, etc. Debian unstable, even experimental, are often months behind on Gnome, for example.
Compare https://distrowatch.com/table.php?distribution=debian and https://distrowatch.com/table.php?distribution=ubuntu and you will realize that all the freshness of Ubuntu is build on top of what is available in Debian unstable.
I don't think this idea of "Debian packages are often very outdated" still applies nowadays. One can add "testing" or "backports" channels in your /etc/apt/sources.lists.d and get "upstream version" software. Even "stable" ships fresh enough software these days.
In the last case you can always get the source, update it and send a nmu back to Debian. Lets not forget that that is how open source works :)