Ubuntu ahead of Debian unstable

Apart from debian stable, testing and unstable branch contains more recent version of software. Ubuntu takes unstable one and maintains its own release system. But my point is for example KDE. KDE 19 is present in Kubuntu latest, while debian unstable is still stuck at 17. So if it's based on Debian unstable, why is Debian so many versions behind? Is the Ubuntu packaging system different? Also can you suggest any 'rolling' distro based on Ubuntu (like debian unstable is rolling)?