Not only fighters, pretty much EVERYONE is rapped in there.
Since you take 6d6 damage per round, that's a 21 damage average.
So the DC to cast a spell in there, whatever the spell, is 10+(6-36, avg 21)+spell level. So, to be sure of casting your spell, you need a modifier of +20 to your concentration check, at level 9, this is quite rare
Not to mention, if oyu know who the casters are, ready actions vs spell and target them with ranged TOUCH attacks, those work
And then... rogue types just die faster....