That JSX element is a function call, not a class that has a render method. If that <ExpensiveComponent /> was a `class ExpensiveComponent extends React.PureCom

That JSX element is a function call, not a class that has a render method. If that <ExpensiveComponent /> was a `class ExpensiveComponent extends React.PureComponent { render() { ... } }` it would not be an issue because diff algorithm can step in. I think people are just recognizing that all of this stuff can be optimized away by a proper compiler and this will soon be done. Nothing stops anyone from figuring out the dependencies and doing proper rerenders without diffing algorithms running on every change.