Just thought I'd pop in and drop my two cents.
Looking over the class idea, it certainly looks interesting. It does seem to have a little less straight damage reduction than the other tanks, but between Counter, Seigan, and the various Combo bonuses that benefit Counter, it seems like it'd still be able to keep up. Not to mention, linking defensive benefits to weaponskill combos makes it quite active, perhaps even moreso than Warrior.
As far as the issue of Tank vs. DPS, I honestly wouldn't care what it is. Samurai has kind of ran the gamut of roles throughout FF, between being an actual job and characters who were built similarly to a SAM, and it's always been enjoyable. I imagine that regardless of what role SE slots it into, they'd be able to figure out a way to make it inventive and unique compared to other jobs in that role.