I do this with my Golden Counter Team. I can go over 1M against thoses lvl80 event bosses.
The team set up is that one and only one for both damages and quick battles.
Camelia is max HP and ATK ampies
Poppy is max DEF ampies
Tartarian Aster is a bit over 50% DEF ampies
Mountain Lily is max DEF ampies and 33% HP ampies
Echeveria is arround 30% DEF ampies with only 42% of bloomed affection and still lvl 72 until Tartarian Aster was max DEF ampies so, I could be back on her.
All the counter girls have maxed Defend Rate Up promotion ability and Camelia has +15% damage turn one.
Basically, Poppy, Tartarian Aster, Mountain Lily and Echeveria are here for counter with the two event girls adding 20% DEF on some of them. Camelia is here for defense bonus and a bit slight offensive presence. Her Evade ability help a lot too because she seems to have a natural taunt on her for mysterious reasons. Don't know why but pests usually attacks her instead of the counter girls.
I'm pretty proud of that team. Certainly not the best but they do really decent damages by themselves considering 4 teams on Nutaku with 4 full ampies Rainbow deal only 100k or 200k more damages on same kind of bosses.