In my experience, product people who know what they are doing have a huge impact on the success of a company, product, or service. They also point engineering efforts in the right direction, which in turn also motivate engineers.
I saw good product people leaving completely destroy a team, never seen that happen with a good engineer or individual contributor, no matter how great they were.
I have yet to find a product person that was not involved in the inception of the idea that is actually good (hell, even some founders fail spectacularly here).
Perhaps I'm simply unlucky.