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
2.) Planner
3.) To-Do's
4.) OneNote
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.