Its well balanced this way. The things you can't do well solo are few, such as having a boat driver working with a gunner (using a bow & arrows etc) or pushing a wheelbarrow behind someone making a road. This is very minor stuff. The flipside is that groups consume an aggravating amount of food and metal, making a group's gear up much more effort -- you can argue that each person doing their part isn't any different from solo but the catch is that some resources are geographically limited at least at first, so you have to branch out farther to get enough for all, which may add quite a bit of effort.