I can imagine a board meeting where an investors asks "so why are you behind on your customer growth this quarter?" and one of the founders says "no one at the company thought those projects were worth doing this quarter, and we're only 'guides' to the planning process so we can't ensure that something like that gets done."
Or a customer asks "why didn't you patch that security hole that we knew about last quarter?" - "no-one thought that project was as worthwhile doing this quarter as a bunch of cool but ultimately less-valuable features, and we are only 'guides' to the planning process so we can't ensure that something like that gets done."
There has to be someone setting specific overall goals and being accountable for hitting them. (Edit: at least if I was an investor / customer / employee of the company, I'd feel better if that was in place)
I'd be curious to hear more about how that's handled!
I get that everyone is afraid of prioritization going out the window without managers, but in my experience (and ymmv), managers are no better than productives at prioritizing. Grown-ups are used to taking responsibility.