When you set the default Dashboard in Moodle appearance settings, all users are affected.
This is really problematic, since all users that made some modification to their Dashboard, lose it.
The proposition is this: to allow some selecting of which user should have their Dashboard updated by the default Dashboard setting or at least which should not. That would be quite an improvement already.
But in my opinion, the best would be to create groups of default Dashboards, besides a standard one. Like this:
Standard: all user's Dashboard, except if the user is in one of the bellow groups (used for students);
Group 1: teacher's Dashboard;
Group 2: tutor's Dashboard;
Group 3: admin's Dashboard.
That way, I could put the users in this groups (which are created by the admin) and set a default Dashboard for which of them.