Actually, i think sending the strongest team to the bottom in E2-8 is the best, it's not seen on the map, but once the mantis brothers have been defeated, the squad con go to the final boss straight. Upper boss is a pretty normal one, so the second or even third squad can kill it, then some "weak" team should clear the random mobs and die at the final boss, hopefully killing one or the 2 scarabs.

I went with 2squads around 50K for the top one, and helper with 55K (being helper means it's higher than that, and he was also using sakura+orchid+camelia, so yeah, extremely high damage output), and cleared absolutely easy, so even if helper wasn't so strong, it should be able to be done as there should be 1 to 3 teams ready to pick the boss with low damage since the bugs don't seem to go that far from their nests and upper boss is not scary. Altough one team is bound to lose a lot of time due to the arrows, so it might eat lots of bugs if all other squads die.

Also, killing the mantis as fast as one can with a fast team is also paramount, as they have a live% based attack and a AOE. Evolved Orchid and Alpinias should be superstars for the bottom team.