My take on Samurai as a tank

[Shippuu]

FF Samurais fits best with DRG type light armor.

Except they dont? Both DRG armor and Tank armor would fit them just fine given past Final Fantasy titles. Samurai in FF have a history of being able to equip heavy armor (even shields too). In FFXI they could also equip heavier armors than DRG. Saying they suit DRG armor more than tank armor is simply untrue. If anything they have an equal stake in both sets.

what's a lot more significant is that there are 3 melee and 4 ranged. and there are lot more fights where you want to keep 4 members away from the boss and 4 members close to spread out AOEs.

Well it's a good thing then that RDM fills in for both slots then. Being a magic wielder on top of being a melee fighter. Its certainly an obvious choice for a new dps job.