Order custom post type by posts with most likes first

Yes, there is — use a meta_query with 2 clauses, one which selects posts having the meta, and the second clause with a 'compare' => 'NOT EXISTS' which selects posts without that meta.

So in your $args array, just replace the 'meta_key' => 'pld_like_count' with this one:

'meta_query' => array(
    // make sure it's OR
    'relation' => 'OR',

    array( // selects posts having the meta
        'key'  => 'pld_like_count',
        'type' => 'NUMERIC',
    ),

    array( // selects posts without the meta
        'key'     => 'pld_like_count',
        'compare' => 'NOT EXISTS',
    ),
),