In a simple example like the author provided maybe is not that obvious but try to imagine an example with a more complex nested syntax and maybe some threading

In a simple example like the author provided maybe is not that obvious but try to imagine an example with a more complex nested syntax and maybe some threading or function composition in it. If you have to modify the behaviour of a specific block of code you only need to edit that structure and your block won't get messy neither requiere special syntax. As you say, If your "!" transaltes to an expression in your language and you are already writting pure functions that compose niceley then I agree that the benefit would be at a syntax level only, the homogeneity of treating all code (macros or runtime) equally.