Is React Fiber a Necessary Precursor to Async?

React fiber was designed to solve the problem of like too much CPU work, you don't want it to block the main thread and get some concurrency so that if you have a large React, low-priority React update, it doesn't end up blocking some higher priority thing. The point is just that there's not just one way to do async like fiber is probably very heavily influenced by the constraints of the DOM. We kind of need cooperative multitasking in order to achieve in order to get anything done in the DOM and doync rendering in the DOM today.