Samurai Job = DPS Job

[Agrotc]

snip

I think it's more that the jobs introduced in Heavensward are all probably going to be related to Ishgard itself except for possibly anything MSK related.
As for DRK fitting more it's probably because it's Dark KNIGHT and Ishgard is the only place we've seen in Eorzea to be using something considered as knights and the aesthetic as we've seen of Ishgard has all been very stereotypical medieval Europe in terms of Aesthetic.