On the contrary. This actually shows that the balance is poor if only characters with top-tier unique skillsets have a chance of succeeding. Furthermore, your main losses were either from trap-based puzzles or from your own teammates. The greatest damage to the group was inflicted by Seliad and Tsukiko, not directly by the palace bosses.
Added 2 minutes later
Heroist, choose Kudo. We need a cute Asian archer.

