This idea of micro-shifts sounds made up. Can you reference any companies that have this setup as an employer-employee relationship?
Your freelance tutoring is not employer/employee work. You're a freelancer. You set your own hours and rates.
Lawyers do not work for multiple law firms, choosing which firm to work for as they see fit. Whereas drivers very often work for both Lyft and Uber (and Postmates or Grubhub, etc) at the same time.
But to go back to the tutoring example: if I was working for a tutoring company, agreed to take clients between lets say 1-5 PM, and the rate was set by the company, would that be similar enough?
What the word "employee" means within the context of California labor laws is probably quite different from what we understand it to mean in everyday conversation. What one can imagine might work in an abstract sense may not be even remotely possible within California's legal framework. What is known to already happen and work well in other states isn't necessarily possible in California, either. (At least not without getting the legislature involved.)