you already gave two. the reason "casters really don't need to do alot in there" is because the quest basically only requires sustained DPS, which casters can't provide in a meaningful way due to lack of SP (or lack of sustained dps spells beyond wall of fire, take your pick).
It is this same reason that bringing more than 1 or 2 casters into those quests is pointless.
Any other quest where the boss fight is substantially harder than the rest of the quest provides a situation where a caster might be forced to sit on the side lines for a large portion of a quest, because they need their SP later.