A Debian derivative it may be, but as the server OS with the biggest market share, and also the most widely used Linux desktop distribution, it's hardly 'yet another'
It's yet another. It still repackages debian unstable, kinks and all. At best it adds value through maketing while piggybacking on Debian's work.
You’re quite right that it’s the server OS with the biggest market share, but I seriously don’t understand why. I get why folks like Ubuntu on their desktops — it’s nice & bleeding edge, with all the latest gee-whiz gadgets and tons of proprietary drivers — but why would they use it on a server? For a server one ought to prefer stability & maintainability, no? And for me, that means Debian.
While technically true, a ubuntu derivative carries, by virtue of ubuntu, a shit ton of non-upstream patches than debian... and, by definition, a shit ton of non-free software than debian.