My team was around 56K that took him out so I guess it matter what your teams true power level is (with equipment incl) and if you use burst power maybe? They took him out and final boss down to half.

Probably because his first battle got dragged out too long or his squad got slapped by too many flies, losing unnecessary hp.

I used solo squad with 70-73k power with Toad Lily so I have no problem at all with bottom route.