In this exercise, it shows us a Venn diagram showing how Mathematics, Computer Science and Domain Expertise come together to form data science.
Do I need an equal level of expertise in each of these parts of data science?
Although the diagram appears to show three equally sized circles, this is not meant to imply an equal amount of expertise required in each part of data science. If each circle was scaled accurately to reflect expertise, more than likely each circle will have different sizes, because most people will have a proclivity skewed toward one or two of the parts.
However, to be successful in the field, one should definitely have at least a good grasp of each of the fundamental concepts of Mathematics and Computer Science, and ideally some Domain Expertise in a particular field.