In my humble opinion, the various task tools are seriously lacking. You can create and manage To-Do's/Tasks in 4 different areas of 365.
1.) Project Site Task List
None of these seem to speak with eachother and I am sure that I speak for many when I say that having to go to four different apps to manage my tasks is rather tedious. We need a way to integrate or push updates between the apps for Tasks. While I understand OneNote wouldn't really connect to the rest for various reasons, I think there still should be some sort of the solution for the rest.
In my perfect world, the new To-Do's app would be the hub for any task assigned to you (whether in Planner or a Project Task List) as well as a location to create separate To-Do's for yourself.
As is, I and our users find the lack of integration between all of the different task managers tedious and many tasks get lost in the shuffle.
Paige Elmore IT Project Manager Charlottesville, VA