Regardless of what it is inferior to, it is a fantastic piece which is available to just be grabbed off AH for a relatively low price tag while PLD's are burning in abyssea this will make a great stop gap.
The PDT-x% ToM sword is beyond worthless and the fact that so many PLDs continue to make it just stuns me.
That aside, even if the PDT-x% ToM sword was somehow a decent sword, it still has a lower DMG rating than the Skeld Sword meaning lower overall Vorpal Blade (in terms of Abyssea) damage, and as such lower overall damage. Your best offhand will be the OATwice Khanda (ToM) sword, or at least the easily obtained Joyeuse. Contrary to popular belief, OA2-4 times is not better (it has a ridiculously low DMG rating) because you can't just ignore your damage in the TP Phase and rely entirely on WS damage.