Thanks for sharing this idea, and we've moved it forward for further discussion as a request to have Dashboard to-do items sort chronologically automatically rather than being sorted first by course. You might also want to add your support to a related idea that asks for more manual control of the to-do list: Re-order the To Do List.
I made a post about this in January 2019. It is still causing me problems and I'm frankly shocked that it hasn't been fixed. On the dashboard I should be able to see all assignments and events in purely chronological order regardless of which class they're associated with.