I think this is a great reason to have a co-founder. I co-founded a company with a domain expert, and her ability to get in front of and understand our target audience was way more important to our startup success than my development ability (and the equity shares reflected that). I mean, we needed each other, but she was far more unique than I was.
The alternative for a developer is you immerse yourself into a different domain, or you build tools for developers. Both of which are good paths, but the former is far more time commitment and latter is more common (and thus more competitive).