Or just add few special mobs which are OK with other 2 classes but expert in killing there specific class

Like shaman pakuna's mob version ( pakuma's apprentice) type can counter & kill mages very easily
Kroger's mob version can easily hunt warrior
And
Vori's mob version or apprentice can nullify rogue attacks & kill rogue very quickly.

So no class can be ignored.

(Don't mind if boss names aren't correct)

Have fun!