If not for the PM, who will speak with the customers, gather, analyze and understand their needs and problems?
There should be a person that drives the product in the right direction based on customer conversations.
In the early stages founder is the product owner.
But as the company grows, the role of the founder/CEO changes. You now build the people, and people build the business.
Engineers or CEOs building features no one asked for is IMHO one of the major reasons lots of tech startups fail.
Awesome idea, cool product, but no one asked for that feature you were building for 2 months. (guilty here myself)