Primal is arguably more about the sandbox than any previous version, the plot mostly faciliates sandbox play outings of hunting gathering fighting and rescuing. The whole being a far more integrated quest than previous iterations. In many ways the big mission plot is the journey of bringing your tribe to a position of dominant safety and possibly towards future integration and assimilation therefore the other missions are all subplots to that overall campaign. It is a simple but effective structure that fits the time period but for people less happy making their own story it may seem less than 3 and 4.