Yea, but WoW had a successful launch of a new class. It starts at lvl 50, namely DK.
Basically a story for a new class doesn't need to be as developed as for the other classes - because that's asking for impossible.
You just need a short story (for an hour or two) which will introduce the class basic game mechanics and push it into Makeb or Shadow of Revan expansion.
This might sound like a cheap excuse, but it is a working design.