To be honest, neither Dylan nor Anna needed to hunt these big mutated animals in person. But the two of them preferred to go out and do it because it was quite boring to stay at home.
Besides, the only time when they could use their abilities to the fullest was when they were fighting against these big mutated animals. It would be too dangerous to use their abilities to the fullest against each other or when they were training.
They didn't want to truly injure the other party.
So these big mutated animals became the best answer.
No one would care even if these big mutated animals were to die in large batches or anything. In fact, the people from the base would be very happy to see a lot of big mutated animals dying before they could harm humans.
It would be better for these big mutated animals to be the one dying rather than the humans.