I've had good luck with using multiple orderby arguments in the past, but now that I'm trying it with dates I'm wondering if there's something I'm missing.

I'm trying to order some posts by an ACF datepicker, and alternatively a text field. The datepicker will return a full date e.g. 9/30/2019 and the text field is optional if they only want to use a year e.g. 2019 as the date.

I'd like to order posts In DESC order as follows (US date format):

9/30/2019 | 2019 | 2018 | 1/20/2017 | 2/10/2017 | 2017 etc

Here is my code

$args = array(
    'post_type'      => 'project',
    'tax_query'      => array(
        array(
            'taxonomy' => 'building_type',
            'field'    => 'slug',
            'terms'    => $terms_array,
        ),
    ),
    'meta_query'     => array(
        'relation'    => 'OR',
        'date_clause' => array(
            array(
                'key'     => 'completion_date',
                'compare' => 'EXISTS',
                'type'    => 'DATE',
            ),
        ),
        'year_clause' => array(
            array(
                'key'     => 'completion_year',
                'compare' => 'EXISTS',
                'type'    => 'DATE',
            ),
        ),
    ),
    'orderby'        => array(
        'year_clause' => 'DESC',
        'date_clause' => 'DESC',
        'title'       => 'DESC',
    ),
    'posts_per_page' => - 1,
);

It doesn't seem to work, and appears to be ordering by title. Adding 'type' => 'DATE' doesn't seem to have any affect. I've tried messing around with the Dsiplay/Return formats on the ACF field as well as the general WP date settings also with no apparent effect.

Am I just missing something or should I try going about this a different way?