I don't remember how I did it but I didn't have as many problems as lvl50. I guess I just send my helper team. It would be good if the tower keep tracks of the team used to clear each stage.
Lvl 61 to 65 is a good part of non fun too. Full of long Evade+Crit+Luck fights. Then there is some very hard Weak level of each types, fun big pests with life drain easily killed by Counter+Crit, an "easy" Hit weak serie of pests for Dendrobium and the ultra hard lvl80.
If I don't count lvl80, nothing is as hard as lvl50.