Coordination vs Completion
Without developing complex routing lists, a simple way to make planner more functional for a hierarchy team or multilevel coordination would be to allow the creator to assign for coordination.
If this box was checked, the person assigned the task could check it 'complete'; however, it will still show as requiring the originator to approve the task prior to being put in the complete box. This would also give the originator the option to send it out to other parties subsequently or simultaneously.
I can not coordinate between plans on planner either; however, teams is not showing up on this version of Microsoft teams yet so I may not have the full picture.