How can have a conditional template tag based on the main loop within a secondary loop with new WP_Query(), using get_template_part()

You can ask the main query directly (which is, in fact, exactly what the is_front_page function is doing).

<?php global $wp_query; ?>
<?php if ( $wp_query->is_front_page() ) : ?>
    <div><?php the_content(); ?></div>
<?php endif; ?>

If you altered the main query, however, refer to the backup.

<?php global $wp_the_query; ?>
<?php if ( $wp_the_query->is_front_page() ) : ?>
    <div><?php the_content(); ?></div>
<?php endif; ?>