Except Planner has no timeline or Gantt charts, despite claiming most of last year, that Gantt charts where on their roadmap. I've found Planner to be nothing more than a glorified Kanban board, which is also something Trello does much better even on their Free Tier using your 1 powerup of a Gantt chart.
Trello does it much better for a small team in a non-enterprise setting. Having to manually add and remove users, and manage external sharing is a huge drag in any bigger environment