Yeah all of Seymour's stuff can't be runic. It's a very good idea to bring someone to stoplock Mortibody, either a healer with the BLK spell Stop, or a dancer using Halting Rumba. A white mage with 4* black access (Yshtola for example) would be best because they can get really high mind for longer duration stop. I'd be glad to do that with Yshtola after casting wall, but that means it's more of a utility slot instead of a healer slot since I wouldn't be doing much actual healing. It's still worth it to completely lock out half of the fight's incoming AoE by disabling mortibody.
Other than that, it's your basic holy weak fight. Boss does fire/ice/lightning/water damage and some non-elem. If you have a water resist armor + gigas armlet combo, that would greatly cut down on incoming damage. If we bring a dedicated stacking debuffer like Vaan or Faris (and stop mortibody) then the fight gets really easy.
The boss does protect on himself often, so if going with a physical team (which we obviously will because lol @ holy magic) then we want someone to slot in a dispel. If we have the holy chain, then we don't even need dispel because we're going to be capping 9999's even through protect with a chain.
So I guess I'm pretty much our Yshtola wall caster every MP battle (which I don't mind, she's my only dived healer) so that's what one of my slots will be. I'd like to bring my complete Marche for the other slot for USB aoe party quickcast buffing goodness.
That means we need 1 or 2 healers (my Yshtola will be busy using stop so won't be healing much). We also want a boost/haste user (Ramza with BSB2 would be good, he could dps with CMD1 after since fight won't last long enough to need to re-cast it). We also want a debuffer to stack MAG breaks on Seymour. There's also a very small chance of petrify, so Astra wouldn't be the worst idea, but the chance is small so we could just ignore it and hope to not get RNG screwed.
I recommend we leave black mages at home because the boss counters black magic with single target flare, which really hurts. Sorry Raines!
Typing this post took probably longer than the fight's going to take us, but hey I'm bored right now
