Abaddon's actually pretty much exactly halfway through from what I can GATHER, based on total number of bosses. Except it's an SMT game so there's a good chance that the last dungeon takes up 30% of the total game time and has most of the bosses so whatever.
So you need at least one person spamming weaknesses, one person on heal duty, and either Gale or Cielo spamming Ziodyne, depending on whether you decided to make the game hard or easy on yourself.
Yes, but three characters spamming ziodyne does less than three character spamming zandyne, because in the latter case you've just cast six spells, and ziodyne is maybe doing 1.3 x zan-family's damage. So that's like 3.9 adjusted damage units compared to 6.