Yeah, but by going in a few times and putting characters in different positions each time you can have the strongest party clear out all of the bosses, although it requires quite a bit of backtracking to do so. I forget how many trips it takes to have one party clear out all the bosses, but it's doable in about six if memory serves correctly. I always found it less irritating simply to level up everyone to the requisite levels though; Tyrannosaur Forest levels your characters up really quickly.