What is the role split between product marketing and brand marketing/other marketing functions in product launches?

In the context of product launches, I see product marketers as the drivers in the early stages and brand, demand and content marketing as key partners in the execution of the launch and providers of critical market feedback. 

Product marketing is responsible for: 

- Deciding and articulating what the launch is, who it's for and how to talk about it

- Getting clarity and product knowledge from the product team

- Articulating and running a GTM process 

- Handing off knowledge at the right times, to the right people

Brand marketing, demand generation and content marketing are responsible for: 

- Articulating which channels are most useful, which ones aren't and why

- Listening to and absorbing information relating to the launch in order to find the right opportunities for the specific launch

- Giving feedback on messaging and positioning, the process, etc. 

- Closing the feedback loop with performance data 

- Testing messaging, target audiences and strategies and bringing that knowledge back to the team

Overall, a good product launch process will leave flexbility for both parties to provide feedback, ask questions and poke holes in the strategy with the goal of making the process itself better, as well as improving the content of the launch.