David Kimura PRO said over 3 years ago on StimulusJS, Active Storage and DropzoneJS :
  I haven't messed around with those options to know if they are making any difference or not. You could always make a custom upload controller, use the new url instead of "this.url" which is taken from the direct upload, and return a variant record. However, you'd still have the full size image stored via ActiveStorage and may need to clean those up periodically.