On the other hand, how do you write a function in a react component that retains its identity between renders (to pass as a prop to a child and not have the child re-render when it changes)? You can't — you need useCallback. Meanwhile in svelte you just... write a function.

They each have their own quirks. Personally I'd rather write language specific if/else (obvious, can't get it wrong) than have to remember to reactify my functions if I want to avoid subtle performance issues.