Replace header with large image on home page only, using Genesis child theme

Well I got it working with a different approach but a good answer that provides insight why the approach in my question didn’t work will be accepted as the answer.

I put this in functions.php for the child theme:

add_action( 'genesis_before_header', 'bob_gray_image', 10 );

function bob_gray_image() {
    if ( is_front_page() ) {
        echo('<div class="bobgrayimage"><img src="https://wordpress.stackexchange.com/images/robert-c-gray-banner-maskbob-sharpen.jpg"></div>'); 
    }
}