If you check the documentation for WP_Query you will notice that post_count, which you are using, returns the number of posts being displayed. That is what you see, but not what you want. found_posts returns the total number of results for the query, which is what you want.
$post_count
The number of posts being displayed.$found_posts
The total number of posts found matching the current query parameters
Note that if your query runs with 'no_found_rows' => true the found_posts value will be 0, and there is a found_posts filter that can effect the result as well.