So the Locust are mutating into Lambent, and the Queen was ok with flooding the Locust Hive or whatever after evacuating as many as they could, because it would also flood and drown the Lambent? Is that correct? Do future games explain why the humans were ok with sinking their last city, or was it for the same reason, Jacinto was worth drowning all of their enemies?
It makes more sense when you go trough the games and books etc. Anyway without spoiling, Jacinto is the last city with approximately 25 million people, the city was going to fall and when it would fall it would be the end for most of them. Letting it sink will destroy atleast a huge group of locust and also gives the humans the ability to evacuate more safely.