How can i force Display names to be the same as Usernames?

You can use the wp_pre_insert_user_data filter.

function wpse_filter_user_data( $data, $update, $id) {
  if( isset( $data[ 'user_login' ] ) ) {
    $data[ 'display_name' ] = $data[ 'user_login' ];
    return $data;
  }
  $user = get_user_by( 'email', $data[ 'user_email' ] );
  $data[ 'display_name' ] = $user->user_login;
  return $data;
}
add_filter( 'wp_pre_insert_user_data', 'wpse_filter_user_data', 10, 3 );

You'll probably want to use Javascript and/or CSS to hide the field too for a better user experience.

$( '.user-display-name-wrap' ).remove();

.user-display-name-wrap {
  display:none;
}

I would do with jQuery:

add_action('admin_footer','myPlugin_fixed_user_name');

function myPlugin_fixed_user_name(){
  ob_start();
  ?>
  <script>
  jQuery(document).ready(function($){
    if( pagenow == 'profile' || pagenow == 'user-edit' ){// up to you decide wether to run on edit user ( made by admin ) also or only on personal profile 
      var uName=$('#user_login').val();
      $('#display_name option[text="'+uName+'"]').attr('selected','selected');
      $('#display_name').attr('disabled',true);
    }
  })
  </script>
  <?php
  echo ob_get_clean();
  }

//To be 100% safe you can also run a function on user profile update:

add_action('personal_options_update', 'my_update_extra_profile_fields');

function my_update_extra_profile_fields($user_id) {
  if ( current_user_can('edit_user',$user_id) )
     wp_update_user( array( 'ID' => $user_id, 'display_name' => $_POST['user_login'] ) );
}