I've found that groups of individual contributors are actually very good on deciding what is important, what they should work on and when, and how to work together to get things done.

Managers can provide a useful role in setting the scene, reminding what the goals of the organisation, the department, and so forth are, and how this connects with what the team is doing. They are perhaps most useful in working with individuals who aren't working well as part of the team at the moment - giving them feedback, mentorship, building bridges, connecting them with people, training, and so forth.

In my opinion, managers hurt more than not if they override the self-organisation of teams, and this most hurts when you need two teams to work together - and one of the managers has (explicitly, perhaps) made it clear that doing things "off the plan" is not appreciated.