TcDisplayController is cached in dynamic_page_cache

Unless you want to give out the same result, you want to do:

    return [
      'charts' => $output,
      '#attached' => [
        // Pushing down data to JS.
        'drupalSettings' => [
          'tc' => $data,
        ],
        // Including our own JS "library". Dependencies for it (like Chart.js,
        // Chart.Scatter and jQuery) are handled by tc.libraries.yml.
        'library' => [
          'tc/tc',
        ],
      ],
      '#cache' => [
        'max-age' => 0,
      ],
    ];