The verdict
For a lean B2B team with shared trackers, manual reports and a few dashboards, I'd pick Sheets. It costs nothing to start, everyone already knows it and it is the quickest way from some data to a view.
Pick Tableau when reporting has turned into a weekly spreadsheet chore, numbers come from several systems and every meeting starts with a debate over whose figure is right. It suits teams with someone to own the data model.
Do not jump early. Tableau is more than a small team needs, and it is only as good as the data behind it. Do not stay too long either. When a sheet becomes the system of record or starts to slow down, it is time to move.