[eldavido]

I think it depends a lot on (1) product complexity and (2) who the customers are.

Stripe has the luxury of a product with straightforward requirements (note this says nothing of the technical architecture/complexity of the product, just what it does -- "process credit cards") and they're building for other developers. In a company like this, it seems easier to prioritize based on developers' understanding of the problem.

Contrast that to a place like Zen Payroll (went to breakfast with a friend who works there today). ZP has to deal with complex tax issues, understand and prioritize feature requests from a huge array of non- to semi-technical customers, and deal with major PII/infosec compliance stuff. These kinds of problems really necessitate having someone on the team who will be the go-to expert for their domain, that can act as a "customer surrogate" in discussions of what's important, how something will be used, the relevant laws/regulations/etc.

So to summarize, I think it's less necessary to have a lot of product managers if you're building a simple product for engineers. The minute you get into complex access controls, security roles, legal/compliance issues, multiple classes of customers, or complex multi-tiered pricing setups, you need a PM to make it all hang together.