As the author of the OP, I must say this is very well put. Part of the problem is that there is no fixed 'role' for the person with the 'deep business expertise and shallow but meaningful data science expertise'. In my experience, it could be a bunch of different people. When I was in a network security startup, this expert would typically be a malware analyst. In other companies, depending on the project, it could be someone from Product, Sales or Marketing. Similar to designers, a data scientist is expected to figure out who the main stakeholders are and get them engaged in the process, instead of the business stakeholder being part of the data science team per se.