The past 10 years I've often been the first employee - or one of the first - joining or building up the company's security organization. The combination of (1) having a specialist skill and (2) being around very few other people with the same skill, naturally leads to a situation where too much clarity can be a bad thing. If a non-specialist define a security role, they will probably screw it up. And that's okay.

If you've worked in startups long enough you eventually get a lot of experience in how to hire people whose expertise you do not understand. As an employer and employee I enjoy the collaborative process of defining the role around the candidates strengths and weaknesses.