How to avoid repeating similar properties for all tds of a table in a wordpress post

…there’s no way to include the style in WordPress posts, at all?

You need to add the style tag to the list of allowed post tags, and also ensure TinyMCE recognises it in the editor:

function wpse_180472_wp_kses_allowed_html( $tags, $context ) {
    if ( $context === 'post' )
        $tags['style'] = array();

    return $tags;
}

add_filter( 'wp_kses_allowed_html', 'wpse_180472_wp_kses_allowed_html', 10, 2 );

function wpse_180472_tiny_mce_before_init( $init ) {
    if ( isset( $init['extended_valid_elements'] ) )
        $init['extended_valid_elements'] .= ',style';
    else
        $init['extended_valid_elements'] = 'style';

    return $init;
}

add_filter( 'tiny_mce_before_init', 'wpse_180472_tiny_mce_before_init' );