When do you start to go from generalists to specialists on a revenue operations team to support stakeholders in marketing, sales and customer success?

I have seen it done the other way around even in my own case. I started with Content & marketing before I went to Business Development and eventually landed in Support and Success. Now as a RevOps leader, I understand each of these functions enough to support operations in each of these teams. So at a Leadership level, I'd prefer someone who has done some of it, if not all, and then is able to oversee all of this. 

If I were to start from RevOps and then specialize in one of the fields, I'd start with Data or Business Systems and then venture into the field whose processes I liked operationalizing the most.