DFFOO [JP] Out of Synergy Seymour vs high DEF and 90% reduction Jegran Lufenia+
33I should preface by saying that my Seymour still has no arts, so he is missing some stats, but despite that I would say his potency is quite good overall barring that one particular follow-up attack.
Jegran boss in Arc 3 Chapter 5 pt 1 is notorious for having insanely high DEF and maximum reduction. On top of that you will have to use stack 2+ debuff to stablize the orb and let him have a turn or push him past thresholds to to refresh the orb by probing his threshold mechanic. He also hits very hard.
Seymour vs Add fights - Early LD follow-up
One of the curious things that Seymour can take advantage of early on in the fight is to use splash dmg or friendlies to push the little add's HP down to 50%. It is fast and easy, so Seymour can enjoy his LD follow-up early into the fight without pushing the boss past 50% for it to proc. This should work on add fights that does not auto-heal or take 0 dmg (i.e. Divine summons: Ifrit, Leviathan and Pandemonium). To reiterate why this works, it is because his LD buff reacts to enemy that is below 50% without the need of attack said target specifically, and the LD buff is the key to unlocking the follow-up.
Seymour himself has a stacking debuff that goes up to 3 when the boss is below 50%. So technically Seymour can deal with the orb himself as soon as you push through the HP thresholds (2 stacks at 80%). I rushed Jegran hard at the end so the orb was tight but ultimately irrelevant.
Potency:
I am honestly surprised that he can hit the 16K BRV dmg mark with Jegran's defence near the end. The only BRV dmg that seems to be lacking is the atrophy follow-up after his EX. That being said that particular follow-up is structured with a ton of BRV hits and 1 HP dumps, so it somehow still makes up for the lack of BRV dmg and deal full HP dmg regardless.
There is one thing that can be further improved is the amount of HP dmg up on the enemy. His LD follow-up hits the full increased BRV dmg but is still very slightly missing the maximum HP dump. It is not a potency issue so may be bring a Sazh CA or have Fang/Paine besides him etc.
EX recharger:
Seymour's strongest and longest chain is his Ex against enemy with under 50% HP. He also does not have EX charged when he enters the battle and it takes a few skills to get to it. He is not exactly a fast character but he definitely is not as slow as Raijin lol. So an initial EX recharge and more EX spam after the 50% mark would speed up his dmg and make him pop off considerably more.
As you can see, my HA+0 Seymour with Gilgamesh BT's help and consistently pump out 1.2 mil+ dmg post 50%. They were able to kill Jegran within 8 orb turns with a summon phase. I would say it is quite a finishing rush with more momentum than how the battle began.
Overall I would say Seymour is quite interesting with a loaded LD that features a great CA ability and utility besides his outstanding battle ending damage phase. He seems to still work as intended with an ordinary party setup against a tough enemy deep into the fight with maximum reduction. So I would say his defining mechanics are well implemented. Add fights would be somewhere he can get an early advantage off of, but otherwise kill fast to kill faster.