Businesses exist solely to solve the problems of others. Domain knowledge required to solve and implement a solution to one of those problems is irrelevant – it can be acquired at any point in time, including after the problem has been identified.

That leaves us with the question: Does the domain knowledge accumulated in a PhD program lead one to later find problems that they would have never otherwise been determined to solve?

My hunch says it depends. Some people will find a solution and then go looking for a problem. Others will find a problem, and then go looking for solution. For the former group, a PhD will be quite valuable, but not so much for the latter group – the chances of them even having studied the right domain in advance is slim.