Never ended up bothering with any of the hefty RNG gambles this game besides some 10% stuff like the Wither and Addle technicks and Ribbons. Fortunately you get a set of each ultimate gear for free in the Henne Mines, so you don't really need to bother with Cerobi shenanigans.

Excalibur is IMO the best weapon in the game and why Knight + Bushi outdamages almost everything else with minimal setup. Ironic though that it cannot be used against Yiazmat and Omega, heh.

If you don't like the grind that is Yiazmat, I got a pretty word for you: Wither. It's the most broken move in the game, and Yiazmat is the one time you really have no reason to feel bad for it especially because the Trial Mode has another Yiazmat fight where he has less than 1/10 of his main game HP and it's actually a pretty okay fight. So no reason to play fair against main game Yiazmat =P

The other remaining marks you listed I don't really remember, they're not as hard as the Behemoth King in any case. Don't think there's much they can do against a simple DPS/Tank/Healer team at this point.