Complex and very long forms won't load

Problem/Motivation

Elements endpoint webform_rest/{webform_id}/elements?_format=json takes forever to load on a very complex webforms.

Proposed resolution

Instead of returning renderable array maybe return simpler JSON ?

The following code load much faster and provides everything needed to build the form on front end.

<?php  public function get($webform_id) {
    if (empty($webform_id)) {
      throw new HttpException(t("Webform ID wasn't provided"));
    }

    // Load the webform.
    $webform = Webform::load($webform_id);

    // Basic check to see if something's returned.
    if ($webform) {
      // Return only the form elements.
      return new ModifiedResourceResponse($webform->getElementsInitialized());
    }

    throw new HttpException(t("Can't load webform."));

  }

Also it is probably a good idea to cache response and use Cache tags to invalidate cache and provide the most recent data.