I used a team of Knight, Mystic Knight (Dark Knight in DS), Summoner and Shaman (Devout in DS), each of them in their early sixties (62, 63), and managed to beat it without too much difficulty. Only the final boss remains a bitch when you just have one healer. But it's entirely possible to beat it without Ninjas and Sages, though some leveling is required. Anything below 60 won't cut it.
This was my team:
This is what we looked like when we beat the game:
As you can see, even with a team in their early sixties, it was a close call.