We carpooled every day to get to know our customers
techinasia.com
techinasia.com
Maybe one way to rephrase the question that might be more common might be:
Is it okay as a co-founder to let another cofounder handle customer development if they're more experienced at doing it? Or as a non-technical founder, is it okay to outsource development?
My experience is this is super common, and as such, if a solo founder is not experienced doing customer development, it would make sense at the very least get help doing customer development.
Specialized cofounders is a much less dangerous situation than outsourced core tasks. There are some events of companies failing or people getting really bad deals because the cofounders didn't all have the complete picture on their heads, but since they normally work in close contact and have the same interests, this is rare. Completely outsorcing those tasks completely remove both the proximity and interests alignment.
Yet, I think you are right in that some service that would watch what I'm doing and tell me "now, you need to do X", "you should have done Y", or "don't ever do Z again!" would be valuable. I'd call that "tutoring", not "outsorcing", and I have no idea if somebody does it.
Anyway, it's a topic that's interesting to me given how bad most startups are at it.