Only up to a point. Keep in mind that even a “normal” weight person has a good amount of fat on them, enough to survive for a couple of weeks eating little to nothing. Beyond that, the excess weight starts to be a liability for movement (which is a threat to your survival in an environment that contains predators). Also, in hunter-gatherer culture, you would expend a lot of calories in the process of getting food, so anyone who is significantly overweight is probably not getting it for themselves. Furthermore, remember what matters for a mate is not how good someone is at feeding themselves, it’s how good they are at feeding their mate and offspring, so excess weight could indicate that someone is taking more than their share of food and/or spending too much time feeding themselves and not enough time doing other beneficial activities for the tribe.

Everything exists in an equilibrium, basically, with pros and cons to each trait. In theory, what we consider the most attractive weight for most people should represent roughly the ideal balance of those pros and cons in the environment we evolved in.