The crew was the last link in the chain
that was my immediate thought as well. Purely legally, both the captain and dispatcher are to blame. But there's probably lots of holes in the swiss cheese, and from an operational perspective, a sub-fleet can be challenging, particularly when it's new for everyone.
It has always struck me a slightly squiffy that a guy who stays on the ground can make and overrule the operating Captain. A simple cross-check, not unheard of in aviation? More pairs of eyes etc. As for "guys who stay on the ground and overrule the captain", if a LAME says "no I'm not going to sign the maintenance release"...no sane captain would feel hurt in his pride and feel overruled...(?)