The real package manager itself comes upstream from Debian; Ubuntu just normally puts fragile GUIs around it. Most of the positives for Ubuntu come from Debian. The Ubuntu specific stuff on the other hand sometimes breaks core functionality like booting off software RAID being broken in 12.x, which has worked fine in Debian for at least a decade.

Generally speaking, a server environment is not the right place to run bleeding edge software. Debian's conservatism is quite sensible when it comes to production server environments, and traditionally (before the whole systemd debacle) they were pretty good at prioritizing stability over the feature of the week demanded by more desktop-centric folks. There's Ubuntu and other derivatives that can cater to their specific needs without compromising the integrity of the distribution in general. And if you have a specific application that requires a more recent version, you can always make use of a 3rd party repository (that you'd of course have carefully vetted first), a binary package, or just rolling your own from source. It makes much more sense to take those extra steps for specific applications than take a blanket approach to rolling out new code all over your production environment.