A thing to keep in mind: in this game not all classes are equally viable in solo play. For example a Rdm with its strong heals might have an easy time beating such a fight, whereas, say a Drg, even though higher dps, but literally no self heal ability, might struggle. And a tank might be able to survive the hard hits, but probably wouldn't be able to do enough dmg to kill the thing.
It would be impossible to balance such solo fights in a way you could clear them with any class.