I think I've hit a wall in terms of whale fights since my first attempt on 17-2 went badly and the second went well only because the RNG was generous (wiped out the normal pests first round and the boss spread its 7-8k damage per hit across the squad during the first boss fight; the whale constantly procced Isana Attack during the super pest fight).

I figure that, at the very least, I'll need Viola or a 6* Pierce Knight like Loquat before trying 17-3.