Drupal 8 - Validate a minimum number of paragraphs

Drupal 8 - Validate a minimum number of paragraphs

/**
 * implements hook_form_node_form_alter()
 * @author Daniel Laufer
 * Add validation to the Resource Center content types.
 */
function mymodule_form_node_form_alter(&$form, FormStateInterface $form_state) {
  $node = $form_state->getFormObject()->getEntity();
  $form['#validate'][] = '_mymodule_node_form_validate';
}

/**
 * Validation function for all content types
 *
 * @return void
 */
function _mymodule_node_form_validate(&$form, FormStateInterface $form_state) {  
  // throw an error if we have less than 2 paragraph entities
  $under_content_paragraphs = $form_state->getValue('field_under_content_sections');
  if (!empty($under_content_paragraphs)) {
    $count_of_related_resources = 0;
    foreach($under_content_paragraphs as $parag) {
      if(isset($parag['subform']['field_related_resources'])) {
        $related_resource_field = $parag['subform']['field_related_resources'];
        foreach($related_resource_field as $item) {
          if(gettype($item) === 'array' && $item['target_id'] !== NULL) {
              ++$count_of_related_resources;
          }
        }
      }
    }
    if($count_of_related_resources === 1) {
      $form_state->setError($form['field_under_content_sections'], 'You cannot select only 1 related resources in the Under Content Section. Please select 2 or more, or select 0 and have it auto-populate.');
    }
  }
}

is there any other way of doing the validation without using form alter hook?