[mambodog]

How did you extract concerns from class components and reuse them previously? Easy and hygienic extraction and composability of concerns literally is something new enabled by Hooks that was not offered by class components.

You're also misrepresenting what the docs say about replacing class components. They're saying that you don't need to replace class components just for the sake of using 'the new thing'. However if there was some concern you wanted to extract from a class component that you could not previously, you absolutely could adapt it to use hooks, and then extract and reuse that concern in another component.