Brother Lyrian, I request your mathematical genius in determining if that sword paired with Brotherhood is the optimum setup for Tidus. I've been wondering what's the best option for his other hand for a while now. I have a second Excalibur in the TM farm group just in case or could give him Genji Blade but another water weapon is probably the best option? Does a unit auto chain with itself in this instance no matter what for auto and physical attacks skills?
Hmm I don't have anything to do with my NRG at the moment so maybe I should bite the bullet and get that sword
It will be brutal but I can just keep it on the side while I play FFXIV.
Adding onto what was already said before....
If you are looking at the strength of Tidus's water attack, then you don't want to to split his attacking element in half by equiping an Excalibur (half water, half light in that scenario).
On the other hand as Alkez and Doctor No pointed out, by equipping the same weapon type in both hands, you give up being able to exploit different weapon masteries on a unit (wielding two swords does not double the benefit of Sword Mastery).
Therefore, assuming you are wielding Tidus's TM sword, to obtain the most ATK benefits via masteries, you would want to equip a non-elemental weapon that you do have a mastery for in the other hand (so that you do not dilute the effectiveness of the water element of the sword).
Very fortunately, by the time Tidus is released, there will be a freebee 103 ATK non-elemental greatsword released with completing the Aurora key set in the back half the current island (so about 2 weeks from now).
Keep in mind (if I'm reading Tidus's loadout in the wiki correctly), that he does not gain innate Sword Mastery for Brotherhood until he receives enhancements (Sun Crest +2).