Ya'll are being silly.
Yes, SAM doesn't have the desirable Critical-Hit based WS that takes advantage of Razed Ruins, like WAR, or MNK, or NIN.
That doesn't mean one can't DD or melee as a SAM in Abyssea, especially in a group. Just because SAM isn't a good job for duo-trio "low-man" farming in Abyssea, doesn't mean it's "useless". Laughable.
In general, the Magic-based Great Katana WS like Tachi:Jinpu will yield higher WS damage numbers in Abyssea, using Magic Damage+ Atmas. However, the WS numbers on Jinpu can be wildly inconsistent. I think an awesome way to take advantage of SAM in Abyssea is to load up on multi-attack Atma and use a high-DPS high-delay Great Katana, like
Kikugosaku. I like to use Voracious Violet, Lion, and Razed Ruins, adding on Pole Grip, Atheling Mantle, and Nocturnus Mail.
If you manage your Store TP gear properly, and use the above gear and Atmas, with Haste/March effects, you can drop two-level self-skillchains left and right in Abyssea, and three-level self-skillchains whenever Sekkanoki or Meditate is up. Does this take some timing/planning and player skill? Absolutely.
Now, realistically, there is no way that a SAM's damage, even with all these tweaks I've recommended is going to keep pace with a Ukon GreatAxe WAR. However, the damage will be formidable, and far, far from "useless" (as one person in this thread stated). If you'd like to take my tactics one step further and tank or co-tank a NM as SAM in Abyssea, I'd urge you to consider revamping SAM merits to decrease your Third Eye recast time. Having a fresh Third Eye available every 25 seconds makes SAM tanking much more sustainable. Another feature to consider taking advantage of is subbing MNK for SAM tanking. I've not tried this yet, but in theory, SAM tanking could benefit from Max HP Boost II, Subtle Blow II, and Counter traits.
Anyways, "in before" lolSAM. I'm not trying to make the argument that SAM is a dominant melee DD in Abyssea, it isn't. But if you apply some critical thinking, and tweak your SAM equipment and tactics, SAM can be formidable, or at least serviceable as a DD in Abyssea.
Over and out.