Estimating how much traffic needs to be handled and what kind of resources it would take to handle it are absolutely part of both of those questions, which in r

Estimating how much traffic needs to be handled and what kind of resources it would take to handle it are absolutely part of both of those questions, which in reality are the same interview problem because a System Design interview isn't a single question but rather a long series of guided questions that cover architecture, scaling, and a lot more.