"1) It’s painfully obvious to co-workers what features are missing and how those features should work. 2) You can look at your largest competitor and copy functionality."

I'm clearly biased, but both of these are very clear indications that someone needs a product manager of some kind! I find that assumptions kill good development decisions and take you down blind alleys. Even if they seem obvious, having someone attack it from a different angle and challenge these assumptions (and prioritise the features around value rather than people shouting) is product 101.

Will you get by without a PM? Sure. Will it be as good as it could be? From experience, no. Does that matter - uh, maybe I guess... depends on your ambitions! I would say that understanding users isn't just about external clients but that having strong Product Management of internal stakeholders for internal tools can be transformative.