It was five Deviants total in the main jungle fight. Also, look at how out of shape professional athletes can get with just a year or two away from their sport. Now think about these Eternals not having to fight anything for over 400 years. They may not have been physically out of shape because their synthetic bodies don't do that, but their mental skills and fighting skills and teamwork skills turned to mush in that time. And also, when they finally get back together to deal with the thawed out Deviants, they have to do it without the one who was their leader for 7000 years. And with a traitor trying to screw them over.